Reasons For Re-Baptism While there isn’t a single example of any one in Scripture being re-baptized, [there is no specific mention of anyone who did not understand baptism] it is not outside of reason to imagine that there are some circumstances in which a person may want to be re-baptized. The reasons for a person to have been baptized could be very varied. For example a person could have been baptized at a very young age without a true understanding of the nature of baptism. Some one else could have been baptized as a prerequisite to joining a particular church. It is also entirely possible for someone to have been baptized in a flood of emotion after a particularly moving altar call. Again it is not unheard of for someone to be baptized because everyone else is doing it. But none of the above is the function of baptism and constitutes an improper understanding of what baptism is for. Therefore if any of the above are true, or if you simply did not understand what baptism is, then it is possible that you just got wet and might consider being re-baptized. And If you are unsure, then there is nothing in scripture that says you should not be immersed again.
What Baptism is Not In Acts 10 Cornelius and his household were saved before being baptized. We know this because they had received the Holy Spirit, which is the evidence of salvation (Romans 8:9; Ephesians 1:13; 1 John 3:24). and the reason Peter agreed for them to be baptized. While baptism does not ‘wash sins away’, the Bible always places believing in Christ for salvation and baptism together. Baptism is commanded in Scripture, which means that although it is not a requirement for salvation, it is an important act of obedience. Peter tells us that it is “the pledge of a good conscience toward God”
What Baptism Is The water symbolizes a spiritual cleansing gained through Christ’s victory over death and is a public demonstration of faith and renewal. In the words of Come Reason Ministries. “… baptism is an act of identification with a person, group or cause. This was well understood in the days of the disciples, for many Greek cults also had baptisms, as did John the Baptist. Like receiving a diploma at a graduation ceremony signifies that one has completed all his required study appropriately, baptism is a sign to others that a change has occurred. The ceremony does not make one a graduate, but is an outward display of what has already happened”. [Does 1 Peter 3 Mandate Baptism?]
Again, let us repeat.. Baptism is commanded in Scripture.. Baptism, like any validating behavior, is "essential to salvation" only in the sense that if you don't want to go through with it, and there is no barrier to understanding, then it is clear that you do not possess salvation. Thought and action are expected to correspond. The conversion and the baptism are regarded as one process, not because the latter is required for salvation, but because it is expected in light of salvation. [Was This Dip Really Necessary? James Patrick Holding]
A Relevant Question Perhaps the most relevant question to be asked is what was your understanding was when you were baptized the first time. While it is not necessary to have perfect knowledge of the Scriptures at the time of baptism, a basic understanding of sin and salvation is. So did you, when you were baptized, believe that you were in sin, felt remorse and self-reproach for those sins and wished to change direction… becoming a follower of the Lord Jesus. And did you believe that your sins would be forgiven through the death and resurrection of Jesus Christ? Repentance for sin and resolving not to continue in it, is a necessary prerequisite to baptism because without it one has no reason to be immersed. If you understood the basics, then there is probably no reason to be baptized again. Footnote: In Acts 19 Paul meets a group of Christians that had already been baptized by John the Baptist and whom Paul re-baptizes in the name of Jesus. It stands to reason that a baptism by John the Baptist, before the death of Christ, would not qualify as a New Testament baptism.. since the baptism before the resurrection and those done when Jesus was still in the beginning stages of His ministry probably had significant differences in terms of why people were being baptized. Which could very well be why Paul re-baptized this particular group of people. [1] And it came to pass, that, while Apollos was at Corinth, Paul having passed through the upper coasts came to Ephesus: and finding certain disciples, [2] He said unto them, Have ye received the Holy Ghost since ye believed? And they said unto him, We have not so much as heard whether there be any Holy Ghost. [3] And he said unto them, Unto what then were ye baptized? And they said, Unto John's baptism. [4] Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus. [5] When they heard this, they were baptized in the name of the Lord Jesus. [6] And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied. | 
