At the end of John 3:3, Jesus makes a revealing statement that contains a significant term: "Unless one is born again, he cannot see the kingdom of God." "See" is the significant word. One's first reaction to the word "see" is to assume a literal, visual observation. However, the Greek word here is eidon (Strong's #1492), which means "to know, be aware, consider, perceive, be sure, and understand." Its usage also includes "behold," "look on," and "see." The Bible frequently uses it in the sense of mental apprehension rather than visual sight, that is, as "I get it," "I understand," or "now I see it."
The apostle Paul is a dramatic example of a man who made a sudden sharp turn in conduct and attitude when he "saw" that he was in reality a hardened sinner and not headed into the Kingdom of God. Here in John 3:3, then, Jesus' emphasis is on the Kingdom of God being something to be understood or comprehended rather than visually observed.
His remark has this sense: "Except a man be born again, he cannot come to know the things of God; he cannot be fitted for it or enjoy its benefits." In this context, He teaches the Kingdom of God as an entity of valuable spiritual and moral force. Vincent's Word Studies of the New Testament, vol. 2, p. 91, explains its intent in this context: "The things of God's kingdom are not apparent to the natural vision. A new power of sight is required, which attaches only to the new man."
John W. Ritenbaugh
Born Again or Begotten? (Part One)