1) Believe That We, Or Our Pastor/Denomination/Spiritual Leader, Cannot Be Fooled
In spite of the fact that deception is one of the major themes of the New Testament, with the words deceit, deceitful, deceitfully, deceitfulness, and deceive, used over and over again, Christians make two very dangerous mistakes. They 1) believe they cannot be fooled. 2) Assume that their pastor, mentor, spiritual leader, or denomination as a whole, cannot be deceived. Although both Peter and Paul were very emphatic about the fact that wolves would come from the flock itself, most Christians today, totally ignoring the implications of Paul's warning in Acts 20 29-30, seem to think that heresy is something that largely happens outside the church.
2) Attribute Every Personal Testimony and “Sign” To Being Of, Or From, God
One of the most dangerous mistakes made in the church is assuming that God must be present because miracles are performed. So one has to ask whether supernatural manifestations provide evidence that God is at work? The short answer is no! There is absolutely no question that personal testimony can be very valuable, but it has it's place, most often as encouragement for believers. Many, many members of cults like the Mormons and Jehovah's Witnesses,etc. can and do give powerful testimonies of how their lives have changed. Numerous members of other religious groups can testify as to how they or someone else was healed by "the power of prayer", by their "guru", or holy man.
3) Take Bible Verses Out of Context
No Biblical author simply strung together a number of lofty sounding phrases disconnected from one another. Since each verse is an integral part of a particular point the author was trying to make, no one should read, much less base their beliefs on, stand alone verses. The reader can only be accurately informed by God's Word the way it is written… in its context. Understanding what the author meant comes not only from the words he wrote, but also by what the overall message of the chapter is intended to convey. But, since this takes a little more time, study and effort, most Christians are content with allowing a verse to be wrested from it's context, and used to convey whatever meaning the speaker/author wishes it to convey.. This, all too often is nothing but a corruption of Scriptures done (intentionally or unintentionally) to persuade men that whatsoever the false teacher says is based on Biblical truth.
4) Believe That We, As Christians Are Not To Judge Anything Or Anyone
Sadly this post modern idea has carried over into the church - Those who quote the 'judge not" statement perfectly illustrate the old saying... "a little knowledge is a dangerous thing" Few seem to realize that this is not a stand alone statement that Jesus pulled out of thin air, then went off to try his hand at fishing for his lunch on the Sea of Tiberias, saying no more on the matter. In fact it has been terribly wrested from it's context (See Section above). If we allow the Lord to complete His thought AND His sentence we will find that that Jesus wasn't saying, or even implying, that we should never make judgments about anyone at any time, but was condemning a certain type of judging. In fact, discernment or "judging" is one of the gifts of the holy spirit
True and False Unity
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. Ignoring important areas in which we differ is simply a papering over of the rot in the walls
The Myth of Faith Alone
Perhaps one of the all time greatest delusions in the Christian world, is the innumerable number of people who are under the impression that, in order to be forgiven their sins, and thus inherit eternal life, all they have to do is believe Jesus died for their sins on the cross. If one were to ask the vast majority of Christians what one has to do to be saved, you would get a number of answers like "accept Jesus as your personal savior", "ask Jesus into your heart" etc (Link Below). However, while the terminology may vary, the answers would almost all boil down to all you have to do is believe... all you have to do is have faith. In other words, at the very moment the sinner puts his, or her, faith in Jesus Christ and accepts Him as his/her savior, that person has entered into a covenant relationship with God, has received God's forgiveness of sins, and the gift of eternal life. In fact the suggestion that anything other than faith is required for salvation, is not only militantly opposed by most of Christendom, but denounced as an unbiblical, works based, false teaching. But is this true? While it is certainly a fact that the Bible teaches that faith is an essential ingredient, without which it is impossible to please God, it never ever teaches that faith is the only requirement for salvation.
Also See Why NOT To Ask Jesus Into Your Heart
The most fundamental, vital question that anyone can ask is what must I do to be saved?... the answer to which is perhaps the most crucial point of the whole New Testament. Yet there are no end of well meaning Christians who, in answer to that life and death question, will inform you that You have to ask Jesus into your heart The burning question is whether this phrase accuratel communicates the truth of Scripture.