That which is born of the flesh is flesh. That which is born of the Spirit is spirit.
Here Jesus is talking about His cross. Notice again the word must. "Even so must the Son of man be lifted up." If there is to be the possibility of redemption, if there is to be an experience of being born again, it can only be by the Son of man being crucified, so must the Son of man be lifted up. He uses a very interesting example out of their history in the Old Testament found in Numbers 2l, where the children of Israel, after their failure to enter into the land, and Moses began to take the route around towards Edom up through Moab and Ammon, coming into the land from the east, the people began to murmur and complain against Moses, saying, "Why did you bring us into this wilderness to die, where there is no bread or water, and our souls loathe this manna? We're sick of it."And the anger of the Lord was kindled against the people of Israel, and God sent these little serpents into the camp, fiery serpents, deadly serpents. They began to bite the people and the people began to die as a result of the bites. And they came to Moses and they said, "We have sinned against you and against the Lord by our murmuring. Pray unto God for us that we might be delivered from this plague of serpents." And Moses prayed unto the Lord and the Lord told him to make a serpent out of brass and to put it on a pole, and to stand it up in the middle of the camp. And it shall come to pass that whenever a man is bitten by one of these fiery serpents, if he will just look at the pole in the middle of the camp, he will be healed, he will live. And so Moses made a serpent of brass, put it on a pole, set it up in the middle of the camp; and it came to pass that whosever was bitten by this serpent, when they looked upon that serpent on the pole, they were healed, they did not die. Therein you find the basis for that little symbol that the doctors use, the serpent on the pole, for healing. But brass in the scripture is always a metal that is symbolic of judgment, and the serpent is always symbolic of sin. So, the brass serpent on the pole was a symbol that God had judged their sins. And by looking at that, they were healed. They did not die.Now, this is an interesting provision that God made, and by what process looking upon the serpent could save a person's life. You know, there's no physical or scientific explanation for this. It was just God's covenant! God's provision. And He said, "All you have to do is look and you will live." Now, I can imagine that there were some hard heads there in Israel, lying on the ground convulsing as a result of the snakebite, about to die. And their friends say, "Hey, in the middle of the camp Moses set up that pole of the brass serpent. Just look at it and you'll be healed." "Don't tell me that, man, that's ridiculous. I can't make sense out of that. How can looking at that do anything for me? Don't you see, I'm dying, man! I need help!" "Yah, but just look!" "Ah, come on, how can that help?" And I can see him arguing and dying because he can't understand how looking would help.