There is a vast difference between a decision for Jesus Christ and a conversion to Jesus Christ. It is a difference between hell and heaven.
Paul Washer describes the difference in this short sermon better than any I have ever come across. Warning! It may make you extremely angry, depending on your school of thought:
If you doubt what Paul Washer says, just turn to Acts 2:14-47 and read the account of how the Church began, especially noting the following verses:
Peter’s words pierced their hearts, and they said to him and to the other apostles, “Brothers, what should we do?” Peter replied, “Each of you must repent of your sins and turn to God, and be baptized in the name of Jesus Christ for the forgiveness of your sins.” All the believers devoted themselves to the apostles’ teaching, and to fellowship, and to sharing in meals (including the Lord’s Supper ), and to prayer. (Acts 2:37-38, 42 NLT)
Search Scriptures yourself and see how John the Baptist and Jesus called people to repentance and for them to continue by sinning no more. Jesus was brutal when he called the religious heretics a brood of vipers.
The following story is about a young man who had made a decision for Jesus, but was unwilling to make a full conversion:
Looking at the man, Jesus felt genuine love for him. “There is still one thing you haven’t done,” He told him. “Go and sell all your possessions and give the money to the poor, and you will have treasure in heaven. Then come, follow Me.” At this the man’s face fell, and he went away sad, for he had many possessions.
(Mark 10:21-22 NLT)
A full conversion is willingness to give it all to Jesus, no matter what He asks of you!