Man must repent (turn from sin) and believe (turn to God). And this happens how for a person?
God said "There is none righteous, no, not one. There is none that understandeth, there is none that seeketh after God. They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one."
So man CANNOT turn from sin and SEEK God. He doesn't even WANT to or UNDERSTAND his doom. Repenting/believing are good things, right? He cannot do anything GOOD.
If salvation depends on man "doing" something, it is not 100% of God.