I believe that he wrote it for the purpose of recommending these books which he was about to write on Offices, in which books he testifies that nothing in the whole range of philosophy is better and more profitable than to give precepts for living. But if this is done by those who do not know the truth, how much more ought we to do it, who are able to give true precepts, being taught and enlightened by God?
(Hom. xxiv. 1) As yet however he was withheld by Jewish infirmity: and therefore he came in the night, being afraid to come in the day. Of such the Evangelist speaks elsewhere, Nevertheless, among the chief rulers also many believed on Him; but because of the Pharisees they did not confess Him, lest they should be put out of the synagogue. (John 12:42)
(Hom. xxiv. 2. in Joan) He did not however conceive any great idea of them from His miracles; and attributed to Him as yet only a human character, speaking of Him as a Prophet, sent to execute a commission, and standing in need of assistance to do His work; whereas the Father had begotten Him perfect, selfsufficient, and free from all defect. It being Christ's design however for the present not so much to reveal His dignity, as to prove that He did nothing contrary to the Father; in words He is often humble, while His acts ever testify His power. And therefore to Nicodemus on this occasion He says nothing expressly to magnify Himself; but He imperceptibly corrects his low views of Him, and teaches him that He was Himself all-sufficient, and independent in His miraculous works. Hence He answers, Verily, verily, I say unto you, Except a man be born again, he cannot see the kingdom of God.
(Hom. xxiv. 2) He says therefore, Except a man be born again, he cannot see the kingdom of God: as if He said, Thou art not yet born again, i. e. of God, by a spiritual begetting; and therefore thy knowledge of Me is not spiritual, but carnal and human. But I say unto thee, that neither thou, nor any one, except he be born again of God, shall be able to see the glory which is around me, but shall be out of the kingdom: for it is the begetting by baptism, which enlightens the mind. Or the meaning is, Except thou art born from above, and hast received the certainty of my doctrines, thou wanderest out of the way, and art far from the kingdom of heaven. By which words our Lord discloses His nature, showing that He is more than what He appears to the outward eye. The expression, From abovea, means, according to some, from heaven, according to others, from the beginning. Had the Jews heard it, they would have left Him in scorn; but Nicodemus shows the love of a disciple, by staying to ask more questions.
This man appears also in the middle of the Gospel, making defense for Christ; for he saith, "Our law judgeth no man before it hear him"; and the Jews in anger replied to him, "Search and look, for out of Galilee ariseth no prophet." Again after the crucifixion he bestowed great care upon the burial of the Lord's body: "There came also," saith the Evangelist, "Nicodemus, which came to the Lord by night, and brought a mixture of myrrh and aloes, about an hundred pound weight." And even now he was disposed towards Christ, but not as he ought, nor with proper sentiments respecting Him, for he was as yet entangled in Jewish infirmity. Wherefore he came by night, because he feared to do so by day. Yet not for this did the merciful God reject or rebuke him, or deprive him of His instruction, but even with much kindness conversed with him and disclosed to him very exalted doctrines enigmatically indeed, but nevertheless He disclosed them. For far more deserving of pardon was he than those who acted thus through wickedness.
(Tr. xi) He had said above that, when He was at Jerusalem—many believed in His Name, when they saw the miracles which He did. Of this number was Nicodemus, of whom we are told; There was a man of the Pharisees, Nicodemus, a ruler of the Jews.
(Tr. xi. c. 3, 4) Nicodemus was one of the number who believed, but were not as yet born again. Wherefore he came to Jesus by night. Whereas those who are born of water and the Holy Ghost, are addressed by the Apostle, Ye were sometimes darkness, but now are ye light in the Lord. (Eph. 5:8)
(Tr. xi. c. 3) What the ground of his belief was, is plain from what immediately follows: For no one can do these miracles that Thou doest, except God be with him. Nicodemus then was one of the many who believed in His Name, when they saw the signs that He did.
(Tr. xi. c. 4) Those then are the persons to whom Jesus commits Himself, those born again, who come not in the night to Jesus, as Nicodemus did. Such persons immediately make professsion.
Therefore, since Nicodemus was of that number, he came to the Lord, but came by night; and this perhaps pertains to the matter. Came to the Lord, and came by night; came to the Light, and came in the darkness. But what do they that are born again of water and of the Spirit hear from the apostle? "Ye were once darkness, but now light in the Lord; walk as children of light"; and again, "But we who are of the day, let us be sober." Therefore they who are born again were of the night, and are of the day; were darkness, and are light. Now Jesus trusts Himself to them, and they come to Jesus, not by night, like Nicodemus; not in darkness do they seek the day. For such now also profess: Jesus has come near to them, has made salvation in them; for He said, "Except a man eat my flesh, and drink my blood, he shall not have life in him."
Nicodemus was one of the many who believed in Jesus, and therefore he came at night, and not during the day because he was not yet illumined with the gracious heavenly light.
His rank is given, A ruler of the Jews; and then what he did, This man came to Jesus by night: hoping, that is, by so secret an interview, to learn more of the mysteries of the faith; the late public miracles having given him an elementary knowledge of them.
[AD 325] Lucius Caecilius Firmianus Lactantius on John 3:1