Deut 10:16

10:16 Circumcise . . . your heart. This verse (along with Deut. 30:6 and Jer. 4:4) is an effective answer to those who imagine that the Old Testament teaches merely a religion of outward form. Circumcision was a symbol, a sacrament, an outward sign of an inward grace. Apart from this, as Paul indicates, circumcision was of no saving significance. True circumcision is “of the heart, by the Spirit, not by the letter” (Rom. 2:29).