48 And seeing him, they wondered. And his mother said to him: Son, why hast thou done so to us? behold thy father and I have sought thee sorrowing.
Origen: The Holy Spirit honored Joseph by the name of father, because he brought up the Child Jesus.
They sought Jesus, lest perchance leaving them he should have returned to heaven, thither to descend when He would. He then who seeks Jesus must go about it not carelessly and idly, as many seek Him who never find Him, but with labor and sorrow.
Gloss: They feared lest Herod who sought Him in His infancy, now that He was advanced to boyhood might find an opportunity of putting Him to death.
49 And he said to them: How is it that you sought me? did you not know, that I must be about my father’s business?
Bede: He blames them not that they seek Him as their son, but compels them to raise the eyes of their mind to what was rather due to Him whose eternal Son He was.
Epiphanius: From His very childhood He acknowledged both the temple and His Father.
50 And they understood not the word that he spoke unto them.
Bede: And they understood him not, that is, the word which He spoke to them of His divinity.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. III (London: Rivington, 1843).