Deuteronomy 10:16 Circumcise therefore the foreskin of your heart, and be no more stiffnecked.
It has always been odd that God would require such a ritual as circumcision. It is an outward symbol of an inward reality: the foreskin of the heart. A hint concerning the meaning is given here: be no more stiffnecked. Don’t resist the grace of God; don’t rebel against the Law of God. Stephen preached to the Jews on the day he was martyred: “You stiffnecked people, uncircumcised in heart and ears, you always resist the Holy Spirit. As your fathers did, so do you [Acts 7:51].”
Moses and Stephen are speaking also to us. A rebellious spirit is a hallmark of a sinner. Children chafe under the authority of parents, and teenagers rebel to break free and seek their own identity, and then stubbornness and rebellion characterize adults all through life. Rebellion is a natural, sinful, human reaction. If unchecked, it will prevent us from faith and salvation.
But the Holy Spirit overcomes our resistance with love, calls us by the Gospel, and persuades us with the truth of the Word. We need to recognize our own sinful stubbornness to appreciate the power of the Gospel and the work of the Spirit. He miraculously turns a stubborn and stiffnecked heart into a soft and good heart that receives the love of God. God’s love is strong enough to soften a hard heart.
Stiffneckedness still resides in a believer’s heart. God loves us enough to break our hearts so that it will receive the love and life of God. Circumcision of the heart, done by the Word and the Spirit, flows into NT Baptism, through which the old man drowns and dies and the Spirit indwells. The New Man has a soft and impressionable heart in which the cross is imprinted.