Paul wrote to the church in Galatia: “the law was our guardian until Christ came, in order that we might be justified by faith.” Perhaps a good living metaphor for this is the relationship we have with right and wrong (not thinking of sin--that's another matter) when we live at home and when we move away from our parents. Mothers and fathers teach us what they believe is right and wrong behavior (and sometimes right and wrong thinking, attitudes, beliefs), and when we are very young we obey them not because we have recognized that their guidance is true, but because they are stronger than we are and also because we know nothing else. We also may love them and wish to please them.
As we get older, we see in the world around other ways of acting, and we may want to do that instead. Sometimes we succeed, but most often we are still bound in different ways to our parents’ way of living. We usually rebel, but only when we are completely free of our parents can we completely “try out” what is different. By then, our parents hope we are rational and mature enough to choose what is truly right, even if that choice means some actions they would not have sanctioned or approved of.
Most often, the rules our parents raise us with are not bad, but it does not take us living long for us to realize that life by rules is not freedom. Freedom is choosing the right rules. Freedom is faithful living in parameters, parameters which may change as we grow.
But Jesus had to make a sacrifice for this difference to come about. Just as we cannot keep all the rules our parents make for us – any child, even a good one, can tell us this – we cannot keep the whole of the law, and so we fall short. Just as good parents love their children when they fall short, so God still loves us. Jesus, our brother, had to sacrifice himself in order for the bonds to be broken. Our parents, if they were good, made sacrifices when we broke the rules, but we could not understand them until we became mature.
When we love Him, the law of God is kept. When we do not love Him, we have only the laws of man, bondage to which makes for failure.