The law in stone tells us not to murder, the law in our hearts tells us not to murder except it defines murder. How do you mean "fulfill the law'? How does this relate to the law?
Brother, if the law is in our hearts, it should our very soul. We shhould see our own wickedness and desire Gods mercy, not only for ourselves, but for all people, because the law condemns all sinners. As David said,
I acknowledge my transgressions: and my sin
is ever before me. Psa.51:3
and,
enter not into judgment with thy servant: for in thy sight shall no man living be justified. Psa.143:2
So the law is fulfilled in leading us to Christ.
One way that the law is fulfilled is that we are forgiven for breaking the law.
Our Lord said,
whatever you want men to do to you, do also to them, for
this is the Law and the Prophets. Mt.7:12
If we don't forgive others who have wronged us, we won't be forgiven. I don't need to cote where Jesus said this. You already know it.
Scripture speaks a lot about obedience, how does obedience relate to fulfilling the law?
When we know we're no better than others and act accordingly (repent, love mercy, etc), we are being obedient to the law.
You give one purpose of the law and you are ignoring loads of scripture giving additional purposes. Have you read the 119th Psalm? It speaks a lot about purposes of the law.
I've read Psalm 119 many times. Nothing I've said is contrary to it. The psalmist isn't saying, "Im righteous because I do every commandment every day." He's saying, "I keep Gods testimony".....that none are righteous.