John Chrysostom

Ver. 4. "But after that the kindness and love of God our Saviour toward man appeared." How? "Not by works of righteousness which we have done, but according to His mercy He saved us, by the washing of regeneration, and renewing of the Holy Ghost." Strange! How were we drowned in wickedness, so that we could not be purified, but needed a new birth? …

Homily on Titus 5 ↗

Theophylact of Ohrid

That is, when the Only-begotten became incarnate and became like us.

Commentary on Titus ↗

Oecumenius

But when the kindness and love of God our Savior appeared, not because of works done by us in righteousness, but according to His own mercy, He saved us through the washing of rebirth and renewal by the Holy Spirit. kindness and love of God our Savior appeared. Through His incarnation. not because of works done by us in righteousness. Not because, Paul says, we live so religiously as to urge him to become incarnate, but because God himself wished to have mercy on us, being unworthy. works done by us. For we did not do it.

Commentary On Titus ↗

Leo the Great

Accordingly let those men cease their complaints who with disloyal murmurs speak against the dispensations of God, and babble about the lateness of the Lord's Nativity as if that, which was fulfilled in the last age of the world, had no bearing upon the times that are past. For the Incarnation of the Word did but contribute to the doing of that which was done: and the mystery of man's salvation was never in the remotest age at a standstill. …

Sermons 23.4 ↗

Thomas Aquinas

Then, he describes the present state of our salvation, when he says, but when the benignity. First, he describes its order and process; second, he confirms what he has said, at it is a faithful saying. In regard to the first he does four things: first, he shows the cause of our salvation; second, the reason he saves, at not by the works of justice; third, the way he saves us, at by the washing; fourth, the end, at that, being justified. …

Commentary on Titus ↗