Nicodemus said unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?
All Commentaries on John 3:4 Go To John 3
Cyril of Alexandria
AD 444
Faith consisteth not, O Nicodemus, in what thou thinkest. Speech sufficeth not unto thee for righteousness, neither wilt thou achieve piety by mere words. For not every one that saith unto Me, Lord, Lord, shall enter into the kingdom of Heaven, but he that doeth the will of My Father Which is in Heaven. But the will of the Father is, that man be made partaker of the Holy Ghost, that the citizen of earth reborn unto an unaccustomed and new life, be called a citizen of Heaven. When He calls the new birth of the Spirit from above, He sheweth clearly that the Spirit is of the Essence of God the Father, as indeed Himself too saith of Himself, I am from above. And the most wise Evangelist again saith of Him, He that cometh from above is above all.
But that the Spirit is of the Essence of God the Father we shall speak more largely in its proper place.