Augustine of Hippo

The circumcision of the heart [refers to] the will that is pure from all unlawful desire; [it] comes not from the letter, inculcating and threatening, but from the Spirit, assisting and healing. Such doers of the law have their praise … not of people but of God, who by his grace provides the grounds on which they receive praise, of whom it is said, "My soul shall make its boast of the Lord," and to whom it is said, "My praise shall be of You."