Moses calls the people to reflect on the covenant and on their relationship with God, which comes first before obedience. God wants us to fear Him first, “fear” being the equivalent word in the Old Testament for a saving faith (Deut. 10:12). This is true relationship, not being scared or terrified. And this is what leads to the next aspect of covenant, which is to walk in God’s ways and to love Him (v. 12). When we are in relationship with God, we naturally want to be close to Him, to follow Him, to walk with Him. And this grows the love in our hearts for Him. As a result, we are led to serve Him with all our hearts and all our lives, which is the same phrase used in Deut. 6 for loving God (v. 12). This is not a service of legalism but a willing, voluntary service of gratitude and joy.
Most powerfully of all, verse 13 is grammatically and theologically an outpouring or consequence of all the elements in the previous verse. When we fear God, walk with Him, love Him, and serve Him with all our hearts, then we will keep the commandments and statutes. But it will be the result of our changed hearts, and not a way to be saved. Not only that, but these commandments are for our good! God rules the universe, and yet He loves us, and that is the foundation of our relationship to Him, and our love in return (vv. 14–15).
However, the people have a problem. Their hearts are not circumcised. They are stiff-necked and stubborn (v. 16). They have not yet given their hearts to God. And so Moses notes that circumcision of the heart is a necessary element to this relationship with God. Fascinatingly, this is the only type of circumcision that is mentioned in Deuteronomy, implying that this is what God wanted all along, and that the outward circumcision was only to represent in a visual and physical way what was going on in the heart. In fact, when God first gave the covenant to Abraham, He did not ask for outward circumcision (Gen. 12:1–3, 15:1–20). It was only after Abraham rebelliously sinned two different times, each related to sexuality and his wife (Gen. 12:10–20, 16:1–16), that God instituted circumcision. Perhaps this was to remind him of where he fell, and where he really needed God’s grace and changing power in his life. But inward circumcision was always the goal, and Deuteronomy’s focus on this alone seems to corroborate this possibility.