Then he isn't a Christian, if he hasn't been saved.
There are plenty of people who have deceived themselves into thinking they are saved.
Is that what you mean?
Either way, he only has to believe.
I don't understand the really, really believe part.
You either believe or you don't.
Who says a believer doesn't sin anymore?
If you have been filled with the Spirit, you will have new desires.
Desires to please God.
You will have His Spirit to help you avoid sin, convict you of sin and help you mature spiritually.
Even tho we still sin, we don't lose our salvation and have to start all over.
Christ intercedes for us 24/7.