The whole of the Bible reveals God’s initiative of conversion and salvation. From the Flood to Abraham to David to Nehemiah to Zacchaeus to Paul, it is clear that God has always been the business of turning people around and starting them anew both on a corporate and individual scale.
In the Old Testament, the emphasis of conversion is especially evident in some texts like Deuteronomy, Jeremiah and Ezekiel. These books each underscore the idea of people wandering in darkness and needing salvation. Each of these three books use vivid metaphors to describe the process by which a person passed from the Kingdom of darkness into the Kingdom of God. Some metaphors refer to God’s gathering of a scattered people, God’s caring for a downtrodden people (Lv 19:34; Ho 2:23), and God’s unfailing love for a repentant people (Jl 2:13; Mi 7:18). But the repetitive metaphor that perhaps most resonates with the familiar New Testament pictures of conversion and salvation is the metaphor of a new heart. Echoing in Jesus’ words to Nicodemus, God in the Old Testament yearns for people to be recreated with a heart that reflects his own love so that they can see his Kingdom and know that God is the LORD. For that reason, God repeatedly urges humanity, specifically through Israel, to turn from their sin and allow him to rework their hearts.
The creation of a new heart is sometimes painted in the lovely term "circumcision." Yikes! In the language of circumcision, the human heart is reshaped through a sacrificial process whereby we are rid of those things that hinder our love for God. In other words, as the metaphor suggests, the unholy is cut off, pruned so to speak, so that the heart can flourish in righteousness. For instance, Deuteronomy 10:16 instructs the Israelites to “circumcise” their hearts in response to God’s love for them. Later on, in Deuteronomy 30:6, the Israelites are assured directly that God himself would perform the circumcision on their hearts so that they would be able to love God with all their heart and with all their soul. Jeremiah 4:4 urges the Israelites to let God circumcise their hearts, admonishing them to comply… or face God’s wrath. The New Testament agrees, saying that a circumcised heart cannot be accomplished through human means, but only is instead brought about through the regenerative change initiated by the Spirit (Ro 2:29).