Galatians 5:14 :
For the whole law is fulfilled in one word, in this: “You shall love your neighbor as yourself.”
The Law is the outward representation of what love does to its neighbor. The Old Testament law is a set of rules that, when you follow them, show what love would act like.
The law is an amazing thing that obviously had to come from someone who was not human. Every law that humans make is either unnecessarily complicated, or lacking. It is often bound to cultural absurdities as well. God’s law He gave through Moses is so amazing in that it defines a relatively simple system that, if it could be followed, would actually make life on earth an amazing and wonderful thing.
The problem with mankind is that we just don’t have love. Listen to how John talks about it:
1 John 4:7-11 :
Beloved, let us love one another, for love is of God; and everyone who loves is born of God, and knows God. He who doesn’t love doesn’t know God, for God is love. By this God’s love was revealed in us, that God has sent his one and only Son into the world that we might live through him. In this is love, not that we loved God, but that he loved us, and sent his Son as the atoning sacrifice for our sins. Beloved, if God loved us in this way, we also ought to love one another. No one has seen God at any time. If we love one another, God remains in us, and his love has been perfected in us.
Do you see how this works? Jesus fulfills the law in us as it says “If we love one another, God remains in us, and his love has been perfected in us.” The way that we can love God and love each other is by the presence of Jesus in us living it out through us. Sure we are doing the loving also, but it is the life of Jesus that makes it possible in us. If we didn’t need the life of Jesus to love each other, then the Law would have been good enough.
The law wasn’t good enough to produce the fulfillment of it in us. That’s what the Messiah came for. He paid the price for our sin and then became our life as we have faith in that life; as we recognize that our old life was crucified with Jesus thousands of years ago.