Theophylact of Ohrid

Another prophecy will also be fulfilled, which says: "They shall look on Him whom they pierced" (Zech. 12:10). For when He comes to judge, then they will see Him in a better and most godlike body, and those who pierced Him will recognize Him and weep. Moreover, this audacious deed of the enemies of Jesus will be a door of faith and proof for unbelievers, as, for example, for Thomas. For he was assured of the resurrection through touching the side.

Commentary on John ↗

Augustine of Hippo

"And hath given Him authority to execute judgment, because He is the Son of man." What judgment, what kind of judgment? "Marvel not at this" which I have said, - gave Him authority to execute judgment, - "for the hour is coming." He does not add, "and now is:" therefore He means to make known to us a certain hour in the end of the world. …

Tractates on John 19 ↗

Jerome

Look at this instance from Zechariah where the Evangelist John quotes from the Hebrew, "They shall look on him whom they pierced." We read in the Septuagint, "And they shall look on me because they have mocked me." In the Latin version, we read, "And they shall look on me for the things that they have mocked or insulted." Here the Evangelist, the Septuagint and our own version all differ. And yet, the divergence of language is atoned for by oneness of spirit.

Letter 57.7 ↗

Thomas Aquinas

2462 The second authority refers to his statement, one of the soldiers pierced his side with a spear, and is taken from Zechariah: They shall look on him whom they have pierced. Our text of Zechariah reads: "They will look on me whom they have pierced" [Zech 12:10]. If we join the statement of the Prophet to what the Evangelist says, it is clear that the crucified Christ is God, for what the Prophet says he says as God, and the Evangelist applies this to Christ. They shall look on him, he says, at the coming judgment. …

Commentary on John ↗