Blessed is the man who remains steadfast under trial, for when he has stood the test he will receive the crown of life, which God has promised to those who love him. Let no one say when he is tempted, "I am being tempted by God," for God cannot be tempted with evil, and he himself tempts no one.
If James stopped there we could still have a way out of the blame. We could say something like, "I can't help it, the Devil made me do it. He tempted me." But, James doesn't start there. Instead he goes right after the deep depravity of man.
But each person is tempted when he is lured and enticed by his own desire. Then desire when it has conceived gives birth to sin, and sin when it is fully grown brings forth death.
The point is that it is our deep desires for sin that causes us to turn trials that we face that are meant to develop good in us (James 1:2-4) into a temptation that causes us to sin. Our faith is tested as God develops character in us to conform us to the image of Christ. However, we often times give in to our desires for sin and turn those tests of faith on their heads and dive deep into the sin of unbelief.
Beloved, we must face up the fact that we are sinners. We must realize that our desires are not naturally for God. The only reason we desire Christ is because God has done a gracious work in us to open our eyes to behold Him. That's how James concludes in verse 18:
Of his own will he brought us forth by the word of truth, that we should be a kind of firstfruits of his creatures.
It is by the will of God that we heard the gospel and were saved. It was God who graciously chose to remove our heart of stone and replace it with a heart of flesh. The depravity of man is deep, but the grace of our God is far more powerful. Praise be to God!