John 21:6

(Hom. lxxxvii) He then gives them a sign to know Him by: And He said unto them, Cast the net on the right side of the ship, and ye shall find. They cast therefore, and now they were not able to draw it for the multitude of fishes.

On that previous occasion Jesus stood not, as here, on the shore, when He gave orders for the taking of the fish, but "entered into one of the ships, which was Simon's, and prayed him that he would thrust out a little from the land; and He sat down therein, and taught the crowds. And when He had left speaking, He said unto Simon, Launch out into the deep, and let down your nets for a draught." There also they put the fishes that were caught into the ship, and did not, as here, draw the net to the shore. By these signs, and any others that may be found, on the former occasion the Church was prefigured as it exists in this world, and on the other, as it shall be in the end of the world: the one accordingly took place before, and the other subsequently to the resurrection of the Lord; because there we were signified by Christ as called, and here as raised from the dead. On that occasion the nets are not let down on the right side, that the good alone might not be signified, nor on the left, lest the application should be limited to the bad; but without any reference to either side, He says, "Let down your nets for a draught," that we may understand the good and bad as mingled together: while on this He says, "Cast the net on the right side of the ship," to signify those who stood on the right hand, the good alone.

A great difficulty in fishing arose for the disciples, so that when the Master came there would be a great height of wonder. He immediately said: "Cast the net on the right side of the boat, and you will find." Twice in the holy Gospel it is read that the Lord commanded that nets be cast for fishing, namely before the Passion and after the Resurrection. But before our Redeemer suffered and rose again, He commands the net to be cast for fishing, but does not command whether it should be cast on the right or on the left; however, appearing to the disciples after the Resurrection, He commands the net to be cast on the right. In that fishing so many were caught that the nets were torn; but in this one both many were caught and the nets were not torn. Who indeed does not know that the good are signified by the right and the wicked by the left? That fishing, therefore, in which it is not specifically commanded on which side the net should be cast, designates the present Church, which gathers the good together with the wicked, and does not choose whom it draws in, because it does not know whom it might choose. But this fishing done after the Lord's Resurrection was cast only on the right, because only the Church of the elect attains to seeing the glory of His brightness, which will have nothing from sinful works. In that fishing the net is torn because of the multitude of fish, because now so many reprobate enter into the confession of faith along with the elect that they even tear the Church itself apart with heresies. But in this fishing both many fish and large ones are caught, and the net is not torn, because the holy Church of the elect, resting in the continual peace of its Author, is no longer torn apart by any dissensions.