Jesus told Nicodemus, “That which is born of flesh is flesh; that which is born of spirit is spirit.” Jesus seemed surprised that He had to clarify something so simple and basic for a learned rabbi like Nicodemus.
It is clear that the spiritual world gives life to the physical world. Take away the spirit from a person and the body begins decaying immediately. Spirit is like the wind: we don’t know where it comes from and we don’t know where it’s going. You can see the effect of the wind (such as leaves moving) but you can’t see the wind itself. Neither can you put the wind in a bottle, for it would then cease to be wind. So it is with the spirit.
Jesus is reminding Nicodemus of what he knows: flesh is impermanent. The kingdom of God therefore cannot be based on flesh, it must be based on spirit. That which is seen is impermanent; that which is unseen (not seen, invisible) is eternal. The kingdom of God must therefore be of an unseen nature – like the wind.
God Himself is spirit – that is, unseen. All the instructions of the Old Testament were written initially for the flesh. This perspective would last only until Messiah would come and reveal its permanent and more important meaning. Thus the Zion that the Lord would inhabit was not a hill in Jerusalem but the “hill”of heaven. The unleavened bread that would nourish the Israelites for their journey would not be wafers but rather sincerity and truth. The manna that would feed them daily would not come from the desert floor but be picked up from the surface of their barren hearts. Thus is the transition of the entire Old Testament, even though we may still be blind to parts of it.
Nicodemus, like most Israelites of his day, was looking for the coming of the kingdom of God. Jesus was trying to wake him up to the fact that this kingdom could not possibly be of the flesh, for if it had, it would subject to the same sort of eventual corruption that had been seen throughout Old Testament history. The kingdom of God, as contrasted from the kingdom of flesh, would come from above and be invisible.
People who serve the church today and hope for its glorification are no different from the contemporaries of Nicodemus who served the temple and hoped for its glorification. That which is born of flesh is flesh.
Since we have all been born of the spirit, let us live by the spirit (Gal 5:25). We were all born of the spirit, not of our own will (John 1:13) but even before we were conceived in our mothers’ wombs (Ps 139). If Jesus warned Nicodemus, who lived on the eve of the kingdom’s coming, not to build on flesh, how much more does He warn us who live in the eternal aftermath of its coming.