Lots of good points in the last few posts.
To put it simply (if possible);
1. The 10 commandments were God's first covenant/contract with his people. Which they failed time and again, to keep their part, hence;
2. Jesus dying for our sins, is God's second, and new contract that completely overwrites the previous one.
A true Christian, should do his best to live right as this pleases God. However, a Christian can not earn forgiveness, or become righteous by trying to keep to both contracts, he must trust in the new one.