2 Corinthians 3:3; 2 Corinthians 3:6

3 being manifested that you are a letter of Christ, cared for by us, written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts.

6 who also made us adequate as servants of a new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.