This is what the LORD says, he who appoints the sun to shine by day, who decrees the moon and stars to shine by night, who stirs up the sea so that tis waves roar - the LORD Almighty is his name: "Only if these decrees vanish from my sight," declares the LORD, "will the descendants of Israel ever cease to be a nation before me." This is what the LORD says: "Only if the heavens above can be measured and the foundations of the earth below be searched out will I reject all the descendants of Israel because of all they have done." declares the LORD. - Jeremiah 31:35-37 (NIV)
God is in control of everything. He is mighty and powerful beyond my wildest imagination. Because of Him the sun rises, the stars shine, and the world turns. God declares that as long as He is God, His people will be His people. God says that He'll always be with Israel's descendants (me, those who follow Christ) and will not reject them, regardless of what they've done.
Often when I mess up and sin, I feel that I have failed God in a huge way. I feel that He surely can't have a use for me, that finally He is done, this was the last straw. But I will strive to turn to God instead of away from Him when I sin. I must come back to His words - to a God that keeps the universe running, I am valuable and he will not turn from me. Turning away from God after we mess up is not the answer - it is when we turn to God in the midst of having nothing to offer that we can more clearly understand the depth of His love and commitment to us.