Deuteronomy covered the times when Moses and the sons of Israel were waiting outside of the Promised Land, where he recounted the happenings, introduced a new set of laws and gave the blessings and curses before he died at 120 years old.
Although it was somewhat a pity that Moses never made it to the Promised Land because of his broken faith with the LORD in the wilderness and that he did not revere the LORD as Holy in the midst of the sons of Israel (Dt 32:51), he did bring out one of the very key messages of the book that was the great commandment in the law (Mt 22:36): that we must “love the LORD your God with all your heart, and with all your soul, and with all your might” (Dt 6:4-5). Moses mentioned this key message again in Chapter 30 that “ the LORD your God will circumcise your heart and the heart of your offspring so that you will love the LORD your God with all your heart and with all your soul, that you may live” (Dt 30:6).
In order to love the LORD with all our heart, soul and might, we must firstly circumcise our hearts and be “no longer stubborn” (Dt 10:16). “Real circumcision is a matter of the heart, spiritual and not literal” (Rom 2:29). This refers to our baptism in the name of Jesus Christ, which brings upon us the gift of the Holy Spirit (Act 2:38) that “cut[s] to the heart” (Acts 2:37). Through the Sacrament of Baptism, the outpouring of the Holy Spirit fills our hearts with God’s love (Rom 5:5) which makes it truly possible for us to obey the law of God because this love is the fulfillment of all the law (Rom 13:10). Therefore, Baptism in the name of Jesus Christ in the New Testament is the “circumcision of our hearts” that was predicted by Moses in Deuteronomy 30:6.