At one level the problem is indeed rejection of God's law. But underneath lies a failure to understand grace and ultimately to understand God. True, his love for me is not based on my qualification or my preparation. But it is misleading to say that God accepts us the way we are. Rather he accepts us despite the way we are. He receives us only in Christ and for Christ's sake. Nor does he mean to leave us the way he found us, but to transform us into the likeness of his Son. Without that transformation and new conformity of life we do not have any evidence that we were ever his in the first place.
At root then antinomianism separates God's law from God's person, and grace from the union with Christ in which the law is written in the heart. In doing so it jeopardizes not simply the Decalogue; it dismantles the truth of the gospel.
-- Sinclair Ferguson, The Whole Christ, p154 (italics original)