Nicodemus responded: "How can a man be born again when he is old? Can he enter the second time into the mother's womb, and be born? " (John 3: 4.)
Christ responded: "Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. That which is born of flesh is flesh: and that which is born of the Spirit is spirit. Marvel not that I said unto thee, Ye must be born again. The wind bloweth where it listeth, and thou hearest the sound thereof, but cannot tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit." (John 3: 5-8.)
Flesh is just flesh. What is required to be able to go where God is will require every person to receive a new Spirit, new life, and become connected with heaven.
Heaven is unruly, unpredictable and blows without predictability. The Spirit is unruly, requiring things which men do not anticipate. It takes you places you have not been before. You cannot just sit within the councils of the Sanhedrin and reason with men's understanding. You must become inspired by a higher source. You must accept that new direction from above, or you will never enter into God's kingdom.
Brilliant. Christ taught the teacher. Now the matter is put to him: Will he receive a new life, and leave the old one? Will he become born again.
How hard it must have been for a man in Nicodemus' position to approach Christ. The fact he came at night testifies to the discomfort of his circumstances. Yet Christ, in patience, told him how to receive eternal life.
What a revealing encounter. We are the richer in our understanding for it having occurred.