The law is written on our hearts, that is, in our own conscience. Living by it frees us from the written law, since it is only an attempt to put the conscience the creator weaved for all of us down on paper. A perfect attempt of course, but still limited by the medium.
The conscience that is united to the Holy Spirit by faith, hope, and selfless charity becomes a mirror of God’s own interior law which is His charity. It become perfectly free. It becomes its own law because it is completely subject to the will of God and to His Spirit. In the perfection of its obedience it “tastes and sees that the Lord is sweet,” and knows the meaning of St. Paul’s statement that the “law is not made for the just man” (I Timothy 1:9)
-Thomas Merton, No Man is an Island, Ch.3 Sec. 10