The Bible often describes our human nature using the term “flesh.” The Greek term is sarx, which is frequently used as a reference to the sin-prone condition of human beings. It’s a poetic reference to our weakness, and our hostility towards God. This is the exact opposite of the Spirit, which is from God (Philippians 3:3; John 1:33). This is the reason that a rebirth is necessary.
The phrase “born again” has become a cliché, so it means very little to most people. However, the difference between the flesh and the Spirit is the reason why rebirth is necessary. Those who are part of “the flesh” are totally incapable of loving, obeying, or knowing God. A sinful human nature makes this impossible. In order to be reunited with God, a person has to have their nature changed. This cannot happen through normal means. It requires that a person be “born again,” this time in the Spirit of God.
John 2:24–3:15 describes a meeting between Jesus and a Pharisee. The last two verses of chapter two highlight the fact that Jesus knew men better than they knew themselves. Nicodemus was the ancient equivalent of a politician, priest, and professor all rolled into one. Jesus proves that this man doesn’t understand religion as well as he’d like to think. In contrast to the loud, public spectacle of clearing the temple, this encounter is a private, night-time meeting. Their actual conversation was probably longer than the brief summary recorded here.
John chapter 3 is one of the most important in the entire gospel. Many crucial ideas are explained in this passage, including the role of Jesus as Savior. After the loud, public commotion at the temple, John transitions to a quiet, nighttime discussion. These verses make it clear that Christ—and Christ alone—is the means of salvation for the entire world. This text also states that those who reject Jesus are rejecting God.