8 But when Simon Peter saw it, he fell down at Jesus’ knees, saying, "Depart from me, for I am a sinful man, O Lord." 9 For he and all who were with him were astonished at the catch of fish that they had taken, 10 and so also were James and John, sons of Zebedee, who were partners with Simon. And Jesus said to Simon, "Do not be afraid; from now on you will be catching men."
Simon, upon realization that he was in the presence of the Lord, was filled with fear, and wished to be removed from the situation. He did not want to have to face the Holiness that is inherent in Christ, in God. The truth of the chasm between his own sinful nature and the absolute holiness of God is too difficult to bear when the realization is made clear.
This corresponds with similar episodes in Isaiah 6:1-6 and Revelation 1:10-18. When men are presented with an understanding of the holiness of God they are gripped with fear of their own transgressions and unworthiness.
In this instance, though, paralleling the other two I mentioned, Jesus immediately responds with words of assurance and comfort. When we recognize God for who he is and repent of our own sinfulness, God is faithful to restore relationship between us.
For me, the intent of this passage is to show us that God is not strictly a God of wrath and judgment, but is merciful to those who are willing to own up to their sins. When Peter said to Jesus, "I am a sinful man," he was admitting that he was not worthy to be in the presence of Christ. Jesus, however, welcomes Peter, knowing full well that Peter is a sinner, and that Peter will deny Christ at the time of his crucifixion.
I believe that God is willing to accept us as we are, but that he loves us too much to leave us that way. He does, however, require repentance of us, recognition of our failings and willingness to turn from them.