1 After this, Jesus shewed himself again to the disciples at the sea of Tiberias. And he shewed himself after this manner. 2 There were together Simon Peter, and Thomas, who is called Didymus, and Nathanael, who was of Cana of Galilee, and the sons of Zebedee, and two others of his disciples. 3 Simon Peter saith to them: I go a fishing. They say to him: We also come with thee. And they went forth, and entered into the ship: and that night they caught nothing.
Augustine: They were not forbidden by their Apostleship from earning their livelihood by a lawful craft, provided they had no other means of living. . . . But how had he not, some one will ask, when our Lord promises, Seek ye first the kingdom of God and His righteousness, and all these things shall be added to you? [Matt 6:33] Our Lord, we answer, fulfilled this promise, by bringing them the fishes to catch.
Gregory: The craft which was exercised without sin before conversion, was no sin after it. Wherefore after his conversion Peter returned to fishing; but Matthew sat not down again for the receipt? of custom. For there are some businesses which cannot or it can hardly be carried on without sin; and these cannot be returned to after conversion.
Chrysostom: They fished in the night, from fear.
4 But when the morning was come, Jesus stood on the shore: yet the disciples knew not that it was Jesus.
Chrysostom: In the midst of their labor and distress, Jesus presented Himself to them.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. IV (London: Rivington, 1845).