Deuteronomy 10:16 and its command for the Israelites to circumcise their hearts, like every other commandment of the Mosaic law, was ultimately given so that the people of God, in trying to circumcise their hearts, would fail and thus look to the Lord to save them (Gal. 3:23–29). They were to trust the One who redeemed them from Egypt to intervene once more and rescue them from the slavemaster of sin, circumcising them in their hearts that they might possess a persevering faith, which the mark of circumcision was supposed to signify. Moses pledged that this final circumcision would happen when Israel returned from exile (Deut. 30:1–10).
Most of the old covenant prophets, it seems, expected this circumcision in the heart to occur immediately after the Jews returned to their homeland (Ezek. 36). The day of the Lord would arrive and the pagan nations would be judged (Obad. 15). Yet God did not bring His plan to a close all at once; rather, He extended the last days to cover the entire period between the first and second coming of Christ (Acts 2:1–21; Heb. 1:1–2). From a human perspective, which is unable to know whom our Father has elected, we can say that His mercy motivated Him to extend the last days so as to gather in those who would not otherwise have been saved if history had ended ages ago.
Since this day has been extended, not everyone in the covenant community who has received God’s mark of ownership is circumcised in the heart. Today’s passage links baptism and circumcision, showing us that new covenant baptism is a proximate fulfillment of the sign of circumcision (Col. 2:8–15). At the consummation, the sign first given to Abraham will be completely fulfilled when the Lord makes a final cut between the sheep and the goats (Rev. 20:11–15). Until then, we apply the mark of the covenant — water baptism — to believers and their children, just as both of these groups were cut out from the world under the old covenant.
Male and female alike receive the mark of baptism in the new covenant as a visible testimony that gender never has and never will give someone an advantage in the eyes of God (Gal. 3:28). This in turn symbolizes that the gates of heaven have been thrown wide open so that all who have been baptized into Christ by faith alone can enjoy all the blessings the Lord has given to His people (Matt. 25:31–46).
John Calvin writes that baptism does not “intimate that our ablution and salvation are perfected by water, or that [it] possesses in itself the virtue of purifying, regenerating, and renewing.” Neither is it “the cause of salvation, but only that the knowledge and certainty of such gifts are perceived in this sacrament” (Institutes 4.15.2). Baptism confirms that those who have trusted in Christ alone are cleansed of sin and set apart for life eternal.