The kingdom, then, is where we enjoy God’s mercy, where the King shares with us His victory over sin and death. Through Christ, God restores us to favor so fully that He makes us His children (John 1:12; 1 John 3:1). That means we become “heirs of God” (Romans 8:17) and “heirs of the kingdom” (James 2:5 cf. Matthew25:34). But first, a child and heir must be born.
The kingdom in the Old Testament had been a physical nation. To be born an Israelite was to be born into the kingdom. Jews could easily see themselves as entitled to a place in the Messiah’s kingdom. But those with such expectations were soon disappointed. John the Baptizer warned them,
Do not begin to say to yourselves, “We have Abraham as our father.” For I tell you, God is able from these stones to raise up children for Abraham. (Luke 3:8)
Nicodemus was a leading Israelite. He belonged to the strictest sect, the Pharisees, and served on Israel’s ruling council (John 3:1). When he met Jesus, his fleshly ideas about the kingdom were quickly corrected (John 3:3-6).
Jesus answered him, “Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God…. Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.” (John 3:3-5)
In the context, John the Baptizer and Jesus were preparing people for the kingdom by calling on them to repent and to be baptized (plunged) in water (John 1:26-28; 3:22-4:2; Matthew 3:2-6; 4:17). The Pharisees denied the necessity of baptism (Luke 7:30). But Jesus insisted that “water” and “Spirit” went together. Without that new birth, entry to the kingdom was impossible.
In repentance and baptism, believers receive forgiveness (Mark 1:4; Acts 2:38), leading to an entirely new way of life. Repentance means a change of heart, which Jesus pictures as denying oneself, dying to one’s own will, and following Him (Luke 9:23-24). His will is that we live like Him, empowered by the Spirit to serve and give generously (John 7:38-39; 13:3-17).