John the Apostle
John 3:3ESV·traditional attribution

Jesus answered him, “Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God.”

John Calvin Reformed @genevareformer

3. Verily, verily, I say to thee. The word Verily (ἀμὴν) is twice repeated, and this is done for the purpose of arousing him to more earnest attention. For when he was about to speak of the most important and weighty of all subjects, he found it necessary to awaken the attention of Nicodemus, who might otherwise have passed by this whole discourse in a light or careless manner.

Matthew Henry Presbyterian @wholebiblehenry

We found, in the close of the foregoing chapter, that few were brought to Christ at Jerusalem; yet here was one, a considerable one. It is worth while to go a great way for the salvation though but of one soul. Observe, I. Who this Nicodemus was. Not many mighty and noble are called; yet some are, and here was one.

Commenting on John 3:1-21

John Gill Reformed Baptist @doctorgill

Nicodemus saith unto him,.... Understanding him of a natural birth, to be repeated: how can a man be born when he is old? as it seems by this, he himself now was: can he enter the second time into his mothers womb, and be born?