God’s law is a plan and prescription for dominion in all of life. It is a statement of the means to victory by Christ’s covenant people in their daily lives, in education, the family, the school, the arts and sciences, our vocations, in church, state, and everywhere else.
R. J. Rushdoony
We study, obey, and teach the law, not to earn our salvation - as if we could take Christ's place - but to grow in sanctification. The law is our tool of dominion, not just over the earth, but over God's enemies as well. Obedience to it is rewarded. It also trains us for citizenship in Christ's kingdom. By it we inculcate Christ's character in ourselves and witness the gospel to others. It orders time and society and regulates every relationship in our lives.
Without the law we are just so many baptized humanists, forever at the mercy of more experienced and evil rebels.