Did Moses preach a different heart circumcision than Paul? Did he preach a different conversion to God? In Paul's words, absolutely not! Moses predicted a society marked by heart circumcision. Paul says that very prediction has been fulfilled (Col. 2:11-13) [Greg Nichols, Covenant Theology: A Reformed and Baptistic Perspective on God's Covenants, 231]
“And now, Israel, what does the LORD your God require of you, but to fear the LORD your God, to walk in all his ways, to love him, to serve the LORD your God with all your heart and with all your soul, and to keep the commandments and statutes of the LORD, which I am commanding you today for your good? Behold, to the LORD your God belong heaven and the heaven of heavens, the earth with all that is in it. Yet the LORD set his heart in love on your fathers and chose their offspring after them, you above all peoples, as you are this day. Circumcise therefore the foreskin of your heart, and be no longer stubborn (Deut. 10:12-16)
It seems a Particular Baptistic Covenant Theology radicalizes the concept of progressive revelation. In Reformed Covenant Theology, the historical covenants are progressive revelations of the one Covenant of Grace. In Nichols' version of Baptistic Covenant Theology, the historical covenants are progressive revelations towards the ultimate expression of the Covenant of Grace. In Reformed theology, each historical covenant do indeed partake of the Covenant of Grace, albeit in a veiled manner. In Nichols' Baptistic Covenant Theology, each progression towards the New Covenant share elements of the Covenant of Grace but each is substantively different from the mature New Covenant. While both hold to progressive revelation, both mean rather different things when they think of progression in God's revelation.
One particular aspect of Nichols' Baptistic Covenant Theology is the view that physical circumcision belongs to physical Israel, and anticipates the heart or spiritual circumcision that marks spiritual Israel, the New Covenant Church. In order for that to be true however, heart circumcision must be future-oriented under the Mosaic economy. It is of course true that Deuteronomy 30:6 shows heart circumcision to be in Israel's future, but is it not also to be a mark of Israel under the Mosaic economy?
Deuteronomy 10:12-16 expresses this command for the Israelites under Moses for their present time. They were to be circumcised in their hearts, which indicates a new disposition towards God, as opposed to being stubborn against Him. Not only were they to be circumcised physically of their foreskins, they were also to be circumcised in their hearts. Their physical circumcisions thus were to be signs of heart circumcisions. Those who have the sign of physical circumcision but not the reality of heart circumcision, as indicated by open rebellion against God and His commands, will to be cut off and excommunicated and exiled from the land (Num. 15:30).
Nichols thus err in locating heart circumcision as a New Covenant reality. In Reformed Covenant Theology, the Old Covenant sign was physical circumcision, signifying heart circumcision. The New Covenant sign is water baptism, signifying Spirit baptism. As Colossians 2:11-13 states, Old Covenant circumcision is replaced with New Covenant baptism. The parallel is not Old Covenant physical circumcision and New Covenant heart circumcision, but Old Covenant physical and heart circumcision, and New Covenant water and Spirit baptism.