23 And John also was baptizing in Aenon near to Salim, because there was much water there: and they came, and were baptized.
[AD 407] John Chrysostom on John 3:22-24
(Hom. xxix. 1) Nothing is more open than truth, nothing bolder; it neither seeks concealment, or avoids danger, or fears the snare, or cares for popularity. It is subject to no human weakness. Our Lord went up to Jerusalem at the feasts, not from ostentation or love of honour, but to teach the people His doctrines, and show miracles of mercy. After the festival He visited the crowds who were collected at the Jordan. After these things came Jesus and His disciples into the land of Judæa; and there he tarried with them, and baptized.

(Hom. xxix. 1) As the Evangelist says afterwards, that Jesus baptized not but His disciples, it is evident that he means the same here, i. e. that the disciples only baptized.

(Hom. xxix. 1) Notwithstanding the disciples of Jesus baptized, John did not leave off till his imprisonment; as the Evangelist's language intimates, For John was not yet cast into prison.

[AD 407] John Chrysostom on John 3:23-24
"And why, when the disciples of Jesus were baptizing, did not John cease to do so? why did he continue to baptize, and that even until he was led to prison? for to say, 'John also was baptizing in Aenon'; and to add, 'John was not yet cast into prison,' was to declare that until that time he did not cease to baptize. But wherefore did he baptize until then? For he would have made the disciples of Jesus seem more reverend had he desisted when they began. Why then did he baptize?" It was that he might not excite his disciples to even stronger rivalry, and make them more contentious still. For if, although he ten thousand times proclaimed Christ, yielded to Him the chief place, and made himself so much inferior, he still could not persuade them to run to Him; he would, had he added this also, have made them yet more hostile. On this account it was that Christ began to preach more constantly when John was removed. And moreover, I think that the death of John was allowed, and that it happened very quickly, in order that the whole attention of the multitude might be shifted to Christ, and that they might no longer be divided in their opinions concerning the two.

[AD 420] Jerome on John 3:23
(Hierom. Ep. c. xxiii. ad Evag.) It matters not whether it is called Salem, or Salim; since the Jews very rarely use vowels in the middle of words; and the same words are pronounced with different vowels and accents, by different readers, and in different places.
And they came, and were baptized.

[AD 430] Augustine of Hippo on John 3:23
"And John also was baptizing in Aenon, near to Salim." A certain lake, "Aenon." How do we know it was a lake? "Because there was much water there, and they came and were baptized. For John was not yet cast into prison." If you remember, I told you why John baptized: because the Lord must needs be baptized. And why must the Lord be baptized? Because many there would be to despise baptism, that they might appear to be endowed with greater grace than they saw other believers endowed with. For example, a catechumen, now living continently, might despise a married person, and say of himself that he was better than the other believer. That catechumen might possibly say in his heart, "What need have I to receive baptism, to have just what that other man has, than whom I am already better?" Therefore, lest that neck of pride should hurl to destruction certain men much elated with the merits of their own righteousness, the Lord was willing to be baptized by a servant, as if addressing His chief sons: "Why do you extol yourselves? Why lift yourselves up because you have, one prudence, another learning, another chastity, another the courage of patience? Can you possibly have as much as I who gave you these? And yet I was baptized by a servant, you disdain to be baptized by the Lord." This is the sense of "to fulfill all righteousness."

[AD 430] Augustine of Hippo on John 3:23
But some one will say, "It were enough, then, that John baptized only the Lord; what need was there for others to be baptized by John?" Now we have said this too, that if John had baptized only the Lord, men would not be without this thought, that John had a better baptism than the Lord had. They would say, in fact, "So great was the baptism of John, that Christ alone was worthy to be baptized therewith." Therefore, to show that the baptism which the Lord was to give was better than that of John, that the one might be understood as that of a servant, the other as that of the Lord, the Lord was baptized to give an example of humility; but He was not the only one baptized by John, lest John's baptism should appear to be better than the baptism of the Lord. To this end, however, our Lord Jesus Christ showed the way, as you have heard, brethren, lest any man, arrogating to himself that he has abundance of some particular grace, should disdain to be baptized with the baptism of the Lord. For whatever the catechumen's proficiency, he still carries the load of his iniquity: it is not forgiven him until he shall have come to baptism. Just as the people Israel were not rid of the Egyptians until they had come to the Red Sea, so no man is rid of the pressure of sins until he has come to the font of baptism.

[AD 430] Augustine of Hippo on John 3:23
But why did John baptize? Because it was necessary that our Lord should be baptized. And why was it necessary that our Lord should be baptized? That no one might ever think himself at liberty to despise baptism.

[AD 444] Cyril of Alexandria on John 3:22-23
After the conversation with Nicodemus had now reached its conclusion, the Divine Evangelist again prepares something else most profitable. For enlightened by the Divine Spirit to the exposition of things most needful, he knew that it would exceedingly profit his readers to know clearly, how great the excellence, and by how great measures, the baptism of Christ surpasses that of John. For it was indeed not far from his expectation, that certain would arise who of their folly should dare to say, either that there was no difference whatever between them, but that they ought to be crowned with equal honours; or, having stumbled into folly even wilder than this, say, that the vote of superiority ought to be taken away from Christ's baptism, and the superiority shamelessly lavished on the baptism by water. For what daring is not attainable by the ill-instructed, or through what blasphemy do they not rush, who rising up against the holy doctrines of the Church, pervert all equity, as it is written? The most wise Evangelist then, that he might destroy beforehand the plea for their vain-babbling, introduces the holy Baptist laying before his disciples the solution of the question. Christ therefore baptizes through His own disciples: likewise John too, and not altogether by the hands of others, nor yet did he baptize in those same fountains, where Christ was manifested doing this, but near to Salim, as it is written, and in one of the neighbouring fountains. And through the very distinction (in a way) of the fountains of waters does he show the difference of the baptism, and signify as in a figure that his baptism is not the same as that of our Saviour Christ: yet was it near and round about, bringing in a kind of preparation and introduction to the more perfect one. As then the law of Moses too is said to have a shadow of the good things to come, not the very image of the things (for the Mosaic letter is a kind of preparatory exercise and pre-instruction for the worship in the Spirit, travailing with the truth hidden within), so shalt thou conceive too of the baptism unto repentance.

[AD 735] Bede on John 3:23
John still continues baptizing, though Christ has begun; for the shadow remains still, nor must the forerunner cease, till the truth is manifested. And John also was baptizing in Ænon, near to Salim. Ænon is Hebrew for water; so that the Evangelist gives, as it were, the derivation of the name, when he adds, For there was much water there. Salim is a town on the Jordan, where Melchisedec once reigned.

The same kind of benefit which catechumens receive from instruction before they are baptized, the same did John's baptism convey before Christ's. As John preached repentance, announced Christ's baptism, and drew all men to the knowledge of the truth now made manifest to the world: so the ministers of the Church first instruct those who come to the faith, then reprove their sins; and lastly, drawing them to the knowledge and love of the truth, offer them remission by Christ's baptism.