An uncircumcised heart is the same as one that will not confess sin and iniquity – one which refuses to repent. In other words, to have an uncircumcised heart is to be unconverted and ungodly. By implication, a regenerate and converted heart is a circumcised heart, in which there is sorrow over sin, repentance, and confession. This is the kind of heart that physical circumcision was to signify. Baptism, likewise, holds the same significance. This meaning for circumcision is seen in Deuteronomy 10.16: “Circumcise, then, your heart and stiffen your neck no more,” and in Deuteronomy 30.6: “Moreover, the Lord your God will circumcise your heart and the heart of your descendants, to love the Lord your God with all your heart and with all your soul, in order that you may live.”
From: Children of the Promise: The Biblical Case for Infant Baptism by Robert R. Booth (Phillipsburg: P&R Publishing, 1995), p. 101.