This is a helpful quote from Richard Gaffin, from his book By Faith, Not by Sight, p. 103:
The gospel is to the end of removing an absolute law-gospel antithesis in the life of the believer.
Briefly, apart from the gospel and outside of Christ the law is my enemy and condemns me.
Because God is my enemy and condemns me.
But with the gospel and in Christ, united to him by faith, the law is no longer my enemy but my friend.
Because now God is no longer my enemy but my friend, and the law, his will, the law in its moral core, as reflective of his character and of concerns eternally inherent in his own person and so of what pleases him, is now my friendly guide for life in fellowship with God.
To be clear, Gaffin is not hear talking about the distinction between the Mosaic Covenant and the New Covenant, but rather between the concepts of “do” and “done”—what Christ has accomplished, and what God wants and enables us to do in the power of his Spirit.