Were John about to converse with us, and to say to us words of his own, we needs must describe his family, his country, and his education. But since it is not he, but God by him, that speaks to mankind, it seems to me superfluous and distracting to enquire into these matters. And yet even thus it is not superfluous, but even very necessary. For when you have learned who he was, and from whence, who his parents, and what his character, and then hear his voice and all his heavenly wisdom, then you shall know right well that these (doctrines) belong not to him, but to the Divine power stirring his soul.
From what country then was he? From no country; but from a poor village, and from a land little esteemed, and producing no good thing. For the Scribes speak evil of Galilee, saying, “Search and look, for out of Galilee arises no prophet.” And “the Israelite indeed” speaks ill of it, saying, “Can any good thing come out of Nazareth?” And being of this land, he was not even of any remarkable place in it, but of one not even distinguished by name. Of this he was, and his father a poor fisherman, so poor that he took his sons to the same employment. Now you all know that no workman will choose to bring up his son to succeed him in his trade, unless poverty press him very hard, especially where the trade is a mean one. But nothing can be poorer, meaner, no, nor more ignorant, than fishermen. Yet even among them there are some greater, some less; and even there our Apostle occupied the lower rank, for he did not take his prey from the sea, but passed his time on a certain little lake. And as he was engaged by it with his father and his brother James, and they mending their broken nets, a thing which of itself marked extreme poverty, so Christ called him.
As for worldly instruction, we may learn from these facts that he had none at all of it. Besides, Luke testifies this when he writes not only that he was ignorant, but that he was absolutely unlettered. As was likely. For one who was so poor, never coming into the public assemblies, nor falling in with men of respectability, but as it were nailed to his fishing, or even if he ever did meet any one, conversing with fishmongers and cooks, how, I say, was he likely to be in a state better than that of the irrational animals? How could he help imitating the very dumbness of his fishes?
Source: Homilies on the Gospel of John (New Advent)