Moses told the children of Israel to circumcise their hearts: "So circumcise your heart, and stiffen your neck no longer." (Deuteronomy 10:16). That’s a strange image. Circumcision refers to removal of the foreskin. What does it mean to “circumcise your heart”?
In Deuteronomy 10:16, Moses compared an uncircumcised heart with a stiff neck. A stiff neck is a biblical idiom that refers to pride and stubbornness. A person with a stiff neck is not flexible. He does not make his will suppliant to God’s instruction.
In Jeremiah 4:3-4, an uncircumcised heart is compared to hard, fallow soil that cannot be cultivated because it has not been plowed:
Break up your fallow ground, and do not sow among thorns. Circumcise yourselves to the LORD and remove the foreskins of your heart. (Jeremiah 4:3-4)
This passage from Jeremiah can be compared to the Master’s parable of the sower who cast seed on four different types of soil. The seed that fell on the unplowed soil did not take root. The seed that fell among the thorns was choked out.
In the Bible, the heart represents the seat of one’s will. The uncircumcised heart is stubborn and inflexible. It does not submit to God’s will. The Word of God cannot bear fruit or even take root in that heart.
A person with an uncircumcised heart is a person whose flesh (physical inclinations) dictates his will. A person with a circumcised heart is one whose flesh has been removed from his will, allowing the Spirit of God to direct the will.
According to Paul, a circumcision of the heart takes place when we trust in Messiah. He says to the Gentiles of Colosse that “in [Yeshua] you were also circumcised with a circumcision made without hands, in the removal of the body of the flesh by the circumcision of Messiah” (Colossians 2:11). He tells the Roman believers that even though a person might not be physically circumcised, he can still have a circumcised heart. He says, “He is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter; and his praise is not from men, but from God” (Romans 2:29).
Those in Yeshua should have a markedly different nature than those without Yeshua. Our will should be suppliant to God’s. Those of us who have experienced the miraculous rebirth that is the work of God’s Spirit within us through the agency of His Son are supposed to have circumcised hearts.