Is God's law relevant to Christians?

From J.I. Packer's introduction to Antinomianism by Mark Jones:

Antinomians among the Reformed have always seen themselves as reacting in the name of free grace against a hangover of legalistic, works-based bondage in personal discipleship. Characteristically, they have affirmed, not that the Mosaic law, under which Jesus lived and which was basic to his own moral teaching, does not after all state God's true standards for human living, but that it and its sanctions have no direct relevance to us once we have closed with Christ. Distinctive to Reformed theology from its birth has been its insistence that salvation, both relationally in justification and transformationally in sanctification, is ours entirely by virture of our grace-given union with Christ in his death and resurrection -- a union that God the Holy Spirit creates and sustains. Within this biblical framework, the key error of antinomianism in all its forms has been to treat our union with Christ as involving in effect some degree of personal absorption into Christ, such that the law as a voice from God no longer speaks to us or of us directly. From this starting point, the phalanx of antinomian teachers has spread out, celebrating different aspects of the assured confidence and joy in Christ that this supposedly biblical move of muzzling the law is thought to have opened for us.