When one contemplates how great God is, one cannot but be struck with how vile man and all man's works are. Even our best works are worth nothing to God, yet we trust in them. But God brings his children from trust in their works to trust only in Him, as Jeremiah says:
23 Thus saith the Lord, Let not the wise man glory in his wisdom, neither let the mighty man glory in his might, let not the rich man glory in his riches:
24 But let him that glorieth glory in this, that he understandeth and knoweth me, that I am the Lord which exercise lovingkindness, judgment, and righteousness, in the earth: for in these things I delight, saith the Lord.--Jeremiah 9:23-24
One of the best illustrations of this in literature is in C. S. Lewis's Prince Caspian. After the 2nd Battle of Beruna, High King Peter introduces Prince Caspian to Aslan:
"Welcome, Prince," said Aslan. "Do you feel yourself sufficient to take up the Kingship of Narnia?"
"I — I don't think I do, Sir," said Caspian. "I'm only a kid."
"Good," said Aslan. "If you had felt yourself sufficient, it would have been a proof that you were not."