In our study of Hebrews chapter ten, we look at the meaning and consequences of "willful sin".
"The law is only a shadow of the good things that are coming - not the realities themselves. For this reason it can never, by the same sacrifices repeated endlessly year after year, make perfect those who draw near to worship. If it could, would they not have stopped being offered? For the worshipers would have been cleansed once for all, and would no longer have felt guilty for their sins. But those sacrifices are an annual reminder of sins, because it is impossible for the blood of bulls and goats to take away sins." NIV translation
In chapter 9, we saw that the blood of Jesus was a sacrifice that was sufficient to remove sin once and for all. Here, we see Paul contrast that to the animal sacrifices that were offered at the temple. Jesus went to the cross once and paid for all sin while these animal sacrifices could not.
When we accept Jesus Christ as the payment for our sins, then, there is no more guilt as the sin debt is paid in full. The animal sacrifices did not remove the sin or the guilt and so had to be continually offered. Are you a Christian that is walking around feeling all guilty about your past sins? Stop it! There is no condemnation or shame for those who are in Christ.
"Therefore, when Christ came into the world, he said: 'Sacrifice and offering you did not desire, but a body you prepared for me; with burnt offerings and sin offerings you were not pleased. Then I said, "Here I am - it is written about me in the scroll - I have come to do your will, O God."'" NIV translation
In this psalm, David was looking back at what God had done in his life as well as looking forward to the coming of Christ. Jesus was the fulfillment and we are the body that it speaks of.
"First he said, 'Sacrifices and offerings, burnt offerings and sin offerings you did not desire, nor were you pleased with them' (although the law required them to be made). Then he said, 'Here I am, I have come to do your will.' He sets aside the first to establish the second. And by that will, we have been made holy through the sacrifice of the body of Jesus Christ once for all." NIV translation
God did not design us to live under the law. The law was given to point us to the need for a Savior. Jesus came and fulfilled all of the requirements of the law and replaced it with grace.