Why Christians Are Deceived
That deception is so rampant in the church can be primarily attributed to just one underlying fact - the vast majority of Christians today are Biblically illiterate.
The Four Most Dangerous Mistakes Any Christian Can Make
1) Believe that we, or our pastor/denomination/spiritual leader cannot be fooled, 2) Attribute every personal testimony and “sign” as being of or from God, 3) Take Bible verses out of context and 4) believe that we, as Christians, are not to judge anything or any one. Not necessarily in that order.
Fraternizing With The Enemy
Few seem to realize that the Christians are commanded to separate themselves from those who teach and practice false doctrine
ON THIS PAGE
Essentials and Non Essentials
True and False Humility
There is little question that the Bible clearly shows that the Father desires unity among believers. For instance
Romans 12:10 - Be devoted to one another in brotherly love; give preference to one another in honor;
1 Corinthians 12:13 - For by one Spirit we were all baptized into one body, whether Jews or Greeks, whether slaves or free, and we were all made to drink of one Spirit.
Philippians - 1:27, 2:2 - Only conduct yourselves in a manner worthy of the gospel of Christ, so that whether I come and see you or remain absent, I will hear of you that you are standing firm in one spirit, with one mind striving together for the faith of the gospel; ... make my joy complete by being of the same mind, maintaining the same love, united in spirit, intent on one purpose.
Ephesians 4:3 - in which Paul tells them to be "diligent to preserve the unity of the Spirit in the bond of peace.
And that we have come a long, long way from the earliest church described in Acts 2. It is no wonder that the last verse says they found "favor with all the people".
They were continually devoting themselves to the apostles' teaching and to fellowship, to the breaking of bread and to prayer. Everyone kept feeling a sense of awe; and many wonders and signs were taking place through the apostles. And all those who had believed were together and had all things in common; and they began selling their property and possessions and were sharing them with all, as anyone might have need. Day by day continuing with one mind in the temple, and breaking bread from house to house, they were taking their meals together with gladness and sincerity of heart, (Acts 2:42-46)
But, one has to remember that these men and women had just experienced Pentecost and were, through the apostles, still witnessing many wonders and signs. It was a new and exciting time with active persecution not yet on on them.
However, recent research on articles on unity in the modern church show that most Christian leaders tend to agree (to one degree or another) that there should be unity in the church - usually pointing to the New Testament passages that speak on the subject.
And, to some extent they are right. Human nature being what it is people, in church or out of it, are all too often self-serving and selfish. They gossip, make power plays, form cliques, envy others etc. etc. The list goes on and on.
When any group of people come together, what you can be sure of is that they will differ drastically in their core personalities and characteristics - how they react to situations, how they perceive things around them etc. etc. etc. This can often make achieving a harmonious relationships very difficult. It takes work - sometimes a lot of work. Too many believers seem to have forgotten that being devoted to one another is a principle found from cover to cover in the Scriptures. As Paul wrote
Put on therefore, as the elect of God, holy and beloved, bowels of mercies, kindness, humbleness of mind, meekness, longsuffering; Forbearing one another, and forgiving one another, if any man have a quarrel against any: even as Christ forgave you, so also do ye. And above all these things put on charity, which is the bond of perfectness. And let the peace of God rule in your hearts, to the which also ye are called in one body; and be ye thankful. (Colossians 3:12-15)
However, although it is impossible that we are going to like everyone we come into contact with, when it comes to other believers we have to remember that we have one enormous factor in common - we are all redeemed by Christ and have all been adopted as God's sons and daughters. Although it can be as difficult as all get-out, we belong to one family and we need to accept the differences between us.
For the body is not one member, but many. If the foot shall say, Because I am not the hand, I am not of the body; is it therefore not of the body? And if the ear shall say, Because I am not the eye, I am not of the body; is it therefore not of the body? If the whole body were an eye, where were the hearing? If the whole were hearing, where were the smelling? But now hath God set the members every one of them in the body, as it hath pleased him. (1 Corinthians 12:14-18)
Although, admittedly, liking someone makes it easier, we don't have to like them to care about them and their well being. We don't have to like them in order to help them if we are able. We don't have to like them to encourage them in their faith.
And certainly our churches shouldn't be divided by racial, cultural, or social differences.
There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. (Galatians 3:28)
See Seeker Friendly, Church Growth Failures in The Bible
However, one can also blow the disunity problem up way out of proportion. For example, Thom S. Rainer the president and CEO of LifeWay Christian Resources says (Emphasis Added)
One of the greatest sicknesses in our churches in America is disunity. Indeed, many of the problems we think we have are really just symptoms of the breakdown of unity in the church. 
But how anyone can say that disunity is one of the "greatest sicknesses" in the churches today beats me. I guess they haven't seen the wholesale apostasy - the deviant beliefs and practices that so many believers are turning to and often literally forcing people out of the churches they once loved and called home..
The idea of unity that many Christian leaders preach and teach is not true unity. True unity is NOT setting aside the areas in which we differ and instead, finding common ground that we can come together on. When churches begin to teach and encourage practises like contemplative prayer, or adopt the seeker sensitive or purpose driven models or bring in heretical speakers, Christians are commanded by Scripture to remove the person from their midst. However if much of the church is moving towards dangerous ideas, the person may have no option but to walk away..
An article on lastdaysministries.org says the following (All Emphasis Added)
It's not wrong to have differing opinions but its wrong to allow these opinions to divide and separate us.
When confronted with those who hold different views from us - from the nuclear arms race to speaking in tongues or the doctrine of eternal security - we're presented with a wonderful opportunity to check our motives. If our personal opinions hinder us from relating to a fellow Christian, then we're forced to conclude that our opinions are more important to us than fellowship with another brother or sister in Christ. 
The above statement makes one HUGE mistake. It assumes that there is no truth that people are required to stand on and defend. That how we interpret Biblical precepts is our "opinion" and it is wrong to let our "opinions" divide us.
In which case, God has given us a useless book and we can, with impunity, chuck our Bibles into the trash.
See Fraternizing With The Enemy
We tend to look on confrontation as something to be avoided at all cost, but the Bible's instructions on how to deal with those who teach and practice false doctrine in the church are very explicit. It is a two step process. The heresy has to be actively confronted and, if not repented of, has to be shunned. The duty of every true believer towards those who profess to be Christians but deny the Word of the
Lord, is to come out from among them. Leaving, or separating oneself from apostasy and heresy is not optional, but commanded.
I would love to know which of the early apostles put wrong teachings into the area of "opinion" and let it go. Much to the contrary, they fought tooth and nail to defend the truth. In Paul's sometimes stern, sometimes sad letter to the Galatians, he wrote
But even if we, or an angel from heaven, should preach to you a gospel contrary to what we have preached to you, he is to be accursed! As we have said before, so I say again now, if any man is preaching to you a gospel contrary to what you received, he is to be accursed! (Galatians 1:8-9)
You foolish Galatians, who has bewitched you, before whose eyes Jesus Christ was publicly portrayed as crucified? (Galatians 3:1)
Note the false teachers Paul spoke about were not dancing around in masks and sacrificing virgins on the altar. They were Judaizers who had apparently persuaded many in the church to keep the Mosaic law and be circumcised. Were Paul's efforts to counter the errors of these false teachers destroying unity, or was it that the false teachers were destroying the foundation of Christianity, lowering it to the outward ceremonial system of pre-Christ Judaism.
And if everything is a matter of opinion and we have to shelve most of our differences and stay united, what in the world was the point of Paul's warning about the wolves in the church that would "draw away the disciples after them". Why was he urging the leaders to stay alert and watch out for these deceivers?
Could it possibly be because he was warning the leaders that they needed to gear up for the knock-down-drag-out battles they would have with the powers of darkness?
"I know that after my departure savage wolves will come in among you, not sparing the flock; and from among your own selves men will arise, speaking perverse things, to draw away the disciples after them. "Therefore be on the alert, remembering that night and day for a period of three years I did not cease to admonish each one with tears. (Acts 20:29-31)
The fact of the matter is that God never intended us to be unified with everyone. Unity is an agreement of sorts - a oneness of mind and purpose. As Amos once wrote "Can two walk together, except they be agreed?" Quite simply we cannot be agreed with everyone.
When dealing with the Pharisees, who were respected religious leaders of the day, Jesus' language can only be called 'harsh'. He called them hypocrites, children of hell, blind guides, fools and blind, serpents, and a generation of vipers. Sadly, His words equally apply to far too many religious leaders of today.
"You brood of vipers, how can you, being evil, speak what is good? For the mouth speaks out of that which fills the heart. (Matthew 12:34)
"Woe to you, scribes and Pharisees, hypocrites! For you are like whitewashed tombs which on the outside appear beautiful, but inside they are full of dead men's bones and all uncleanness. (Matthew 23:27)
"You serpents, you brood of vipers, how will you escape the sentence of hell? (Matthew 23:33)
John, the "apostle of love" did not mince any words when speaking of people who claimed to know Jesus, but did not obey Him. He flat out called them "liars".
By this we know that we have come to know Him, if we keep His commandments. The one who says, "I have come to know Him," and does not keep His commandments, is a liar, and the truth is not in him; but whoever keeps His word, in him the love of God has truly been perfected. By this we know that we are in Him: (1 John 2:3-5)
Paul called the Colossians to unity and holiness (Colossians 3:8-15) but that did not mean that the Colossians were simply to love and be patient with each other, for his very next words were...
Let the word of Christ richly dwell within you, with all wisdom teaching and admonishing (Gr. noutheteo) one another with psalms and hymns and spiritual songs, singing with thankfulness in your hearts to God. (Colossians 3:16)
The word translated admonish, is the Greek noutheteo, which means to reprove or warn, which Paul uses several times. He not only admonished many of the churches he was involved with, but instructed many of them to admonish each other.
The epistles also show that he publicly refuted teachings that deviated from God's word.. As he told Timothy
The Lord's bond-servant must not be quarrelsome, but be kind to all, able to teach, patient when wronged, with gentleness correcting those who are in opposition, if perhaps God may grant them repentance leading to the knowledge of the truth, and they may come to their senses and escape from the snare of the devil, having been held captive by him to do his will. (2 Timothy 2:24-26)
When Paul advised gentleness, it did not mean that Timothy was never to confront those who opposed them but that he was to do it with kindness.
Although doctrine has often been allowed to divide people in disgraceful ways, division is not something that can be avoided. you could scour the Scriptures for the next ten years without finding a single word about being united at the expense of truth. On the contrary, since all too often what passes for "unity" is nothing but compromise, Christians are commanded to separate themselves from those that believe and teach false doctrine. They are to refuse to have fellowship with those who cross over the line. It is far better to be divided by truth than united in error.
When Christians obey the Bible and separate themselves from heretics, they are actually promoting genuine Christian unity by standing together against heresy.
See The Four Most Dangerous Mistakes Any Christian Can Make
1) Believe that we, or our pastor/denomination/spiritual leader cannot be fooled, 2) Attribute every personal testimony and 'sign' as being of or from God, 3) Take Bible verses out of context and 4) believe that we, as Christians, are not to judge anything or any one. Not necessarily in that order.
Essentials and Non Essentials
Christian leaders often tell us that there are primary matters on which we have to be agreed - and secondary matters that should not keep us from being united. As said by Steven J. Cole on Bible.org (Emphasis Added)
We should welcome into church membership all whom Christ has saved as long as those with differing views on secondary matters agree not to cause factions over those differences. While we may hold differing views on baptism, charismatic gifts, prophecy, etc. these should not keep us from being one body in Christ. For this reason, we allow those who do not share our Baptist views on baptism to join this church as long as they don't promote or teach their different views here. And, we restrict the office of elder to those who hold to our Baptist views. The same is true of those who hold to the validity of the charismatic gifts for today. We are skeptically cautious regarding most modern expressions of the gifts of tongues, interpretation of tongues, healing, miracles, and prophecy. Those who hold a different view are free to join us as long as they do not promote their views and cause division.
He also says that there are "three broad levels" of Bible doctrine (Emphasis Added)
(a) Essential truths, necessary for salvation. To deny any of these would be heresy and a denial of the faith. These include: The inspiration and authority of the Bible; the trinity; the full deity and humanity of Jesus Christ; His substitutionary death on the cross; His bodily resurrection and second coming; and, salvation by grace through faith alone, apart from works. 
I am sorry, but someone is going to have to show me where the Bible says that belief in the Trinity is essential to salvation. In fact someone is going to have to show me where the Bible teaches the doctrine of the Trinity at all. The pronoun 'He' that the English New Testament uses for the Holy Spirit only reads that way because the original Greek word was translated according to pre-bias and doesn't necessarily say 'He'. And there is more - lots more. including the Greek philosophers who had great influence on the council of Nicea and brought their idea with them. See Is God a Trinity? Additionally, while there is no question that a person is saved through faith alone, one has to be careful here because, as James said Faith without works is dead.
Additionally, the matter of Tongues and their interpretation, Being Slain in the Spirit, Contemplative prayer, Labyrinths and Halloween, cannot simply be put down to a difference of opinion and left at that because these are highly dangerous practices that have been directly derived from the occult. See Mysticism and Doctrines of Demons in The Church
Does anyone seriously think that learning the ways of the pagan world around us is NOT going to affect salvation when God so clearly stated "... come out from their midst and be separate," says the Lord. "and do not touch what is unclean; And I will welcome you. (2 Corinthians 6:17)
The obvious implication being that if we do not separate ourselves from the world, we will not be received, i.e. not saved.
See Why Christians are Deceived
The reasons that so many modern day Christians are deceived are numerous. They believe they should be "united", and are commanded to "love". They do not want to be labeled "heresy hunters", accused of quenching the spirit, or found guilty of 'touching' the Lord's anointed etc. etc.
Very Important Non-essential Doctrines
Some of the issues usually categorized as non-essential can be extremely dangerous.
For example, I cannot count the number of people who have made statements to the effect that because they were taught God alone chooses who will and will not be saved, how they lived their lives made no difference to their salvation which was set in stone. Tragically, this conclusion is a natural outcome of Calvinism. And yes, I know that virtually all Calvinist preachers teach holiness but after all why should anyone bother living their lives on the straight and narrow if all they will lose by going out and having 'fun' is a reward or two..
Those who whole-heartedly believe that they are going to be wafted away on a cloud before the tribulation are going to get the shock of their lives when they find themselves smack-bank in the middle of it. How many will then lose faith imagining that the Bible lied to them? When Jesus said that a coming epoch will mirror Noah's day, not understanding who the 'sons of God' in Genesis were is also going to leave people woefully unprepared.
True and False Humility
Finally, I cannot understand why virtually all the authors I have quoted seem to think that it is pride that makes us want to be right on every issue - And that we should not stand on our "perfect opinion" but concede that the other person might be right. Matt Slick, President and Founder of the Christian Apologetics and Research Ministry states,
It is all right to have differences of opinion on the non-essential matters like worship styles or days, pre-trib rapture, post-trib rapture, Arminianism, Calvinism, etc. Whether you believe one or the other, do not affect salvation. Yet far too many Christians use these non-essential differences as justification for division and sometimes even insight (incite?) anger. When this occurs, the love of God in our hearts is sacrificed to our pride. Instead of saying to one another, "I am right and you are wrong," we should be saying something like, "It is certainly possible that you are correct.
He goes on to ask "Should we not sacrifice our "perfect" opinion on a biblical matter for being gracious to another brother or sister in Christ?" 
Why in the world does virtually everyone assumes that the truth of virtually every matter cannot be known from God's word? No one knows everything. However, God does and He put much of it down in a book that everyone can read. If you choose to interpret a great part of this book according to skewed teachings that have been handed down from generation to generation under the guise of orthodoxy, that is your business.
But, if you can tell someone with possibly dangerous opinions that they may be correct, you are not at all sure of what the Bible teaches or you are not at all honest. You are certainly not doing them any favors.
 Thom S. Rainer. Fourteen Key Reasons for the Breakdown of Church Unity.
 Floyd McClung. True & False Unity. Are We Fighting The Wrong Battles?
 Steven J. Cole. The Unity of the Church. https://bible.org/seriespage/lesson-4-unity-church-john-1722-23-1-cor-1213-eph-41-6-13
 Matt Slick. The need for unity in the church. https://carm.org/need-unity-church