The God-fearing characters of the Bible seem flawless. Then you look again and see that Moses who is referred to in the Bible as a man and a servant of God actually refused to speak for Him. Noah, who walked with God, got inebriated. In the Old Testament, men were polygomous, including the wise King Solomon. The biggest example of sinfulness among the faithful is King David. He committed adultery then murdered her husband. This was a man who was after God's heart.
Anyone who thinks that they are not good enough to become a Christian needs to look again. These Bible characters are considered great because they believed that there is nothing that God cannot do. Even though this does not take place quickly as is evidenced by the above examples, God does perfect the imperfect. He purifies the impure and makes holy His children.