Some counter-intuitive insight:
The root of [Eve’s] antinomianism (opposition to and breach of the law) was actually the legalism that was darkening her understanding, dulling her senses, and destroying her affection for her heavenly Father.
…what the Serpent accomplished in Eve’s mind, affections, and will was a divorce between God’s revealed will and his gracious, generous character. Trust in him was transformed into suspicion of him by looking at the “naked law” rather than hearing “law from the gracious lips of the heavenly Father.”
…legalism and antinomianism are, in fact, nonidentical twins that emerge from the same womb.
…legalism and antinomianism seem to be simple opposites–all that is needed, it seems, is right doctrine. But the more basic issue is: How do I think about God, and what instincts and dispositions and affections toward him does this evoke in me?
It cannot be too strongly emphasized, therefore, that everyone is a legalist at heart. Indeed, if anything, that is the more evident in antinomians.
-Sinclair Ferguson, The Whole Christ