John Chrysostom

But the name John is also interpreted the grace of God. Because then by the favour of Divine grace, not by nature, Elisabeth conceived this son, they engraved the memory of the benefit on the name of the child.

Catena Aurea by Aquinas ↗

Theophylact of Ohrid

Zechariah, being unable to make known to them by signs, asks for a tablet; and when regarding the name of the child he was found to be in complete agreement with his wife, "all marveled," for this name was not in their kinship, and no one could say that the two of them had agreed upon this beforehand.

Commentary on Luke ↗

Bonaventure

And because he could not respond with his voice, he spoke by hand and by letters; and therefore it is added: And asking for a writing tablet, he wrote, saying: John is his name: as if to say: I do not impose a name, but I declare one already imposed; above in the same chapter: "You shall call his name John," according to that passage of Isaiah forty-nine: "The Lord called me from the womb, from the bowels of my mother he remembered my name." And rightly it is said written on account of its indelible firmness, to show that his name is …

Commentary on Luke, Chapter 1 ↗