Look, 2 questions -

1) Why do some truely believe the Gospel and enter into a sincere and lasting state of complete repentance/conversion while others completely reject the Gospel outright, or have not been exposed to the true Gospel or any Christian Gospel message for that matter, or are simply lukewarm in their christian beliefs? Basically what I'm asking is - what makes man to differ?

2) Why did God permit sin to enter the world? Does it serve some type of purpose??? (Again please consider God's attributes!)

The mercy of God is necessary not only when a person repents, but even to lead him to repent, Augustine