2 The inquiry is usually made in connection with this fishing of the disciples, why Peter and the sons of Zebedee returned to what they were before being called by the Lord; for they were fishers when He said to them, “Come after me, and I will make you fishers of men.” And they put such reality into their following of Him then, that they left all in order to cleave to Him as their Master: so much so, that when the rich man went away from Him in sorrow, because of His saying to him, “Go sell that you have, and give to the poor, and you shall have treasure in heaven, and come follow me,” Peter said unto Him, “Lo, we have forsaken all, and followed You.” Why is it then that now, by the abandonment as it were of their apostleship, they become what they were, and seek again what they had forsaken, as if forgetful of the words they had once listened to, “No man, putting his hand to the plough, and looking back, is fit for the kingdom of heaven”? Had they done so when Jesus was lying in the grave, before He rose from the dead—which of course they could not have done, as the day whereon He was crucified kept them all in closest attention till His burial, which took place before evening; while the next day was the Sabbath, when it was unlawful for those who observed the ancestral custom to work at all; and on the third day the Lord rose again, and re called them to the hope which they had not yet begun to entertain regarding Him—yet had they then done so, we might suppose it had been done under the influence of that despair which had taken possession of their minds. But now, after His restoration to them alive from the tomb, after the most evident truth of His revivified flesh offered to their eyes and hands, not only to be seen, but also to be touched and handled; after inspecting the very marks of the wounds, even to the confession of the Apostle Thomas, who had previously declared that he would not otherwise believe; after the reception by His breathing on them of the Holy Spirit, and after the words poured from His lips into their ears, “As the Father has sent me, even so send I you: whose soever sins ye remit, they are remitted unto them; and whose soever ye retain, they are retained:” they suddenly become again what they had been, fishers, not of men, but of fishes.
Source: Tractates on the Gospel of John (New Advent)