Augustine of Hippo — as excerpted in the Catena Aurea on John 14:12-14

“(Tr. lxxi. 3) But what are these greater works? Is it that the shadow of the Apostles, as they passed, by, healed the sick? It is indeed a greater thing that a shadow should heal, than that the border of a garment should. Nevertheless, by works here our Lord refers to His words. For when He says, My Father that dwelleth in Me, He doeth the works, what are these works but the words which He spoke? And the fruit of those words was their faith. But these were but few converts in comparison with what those disciples made afterwards by their preaching: they converted the Gentiles to the faith. Did not the rich man go away sorrowful from His words? And yet that which one did not do at His own exhortation, many did afterwards when He preached through the disciples. He did greater works when preached by the believing, than when speaking to men’s ears. (lxxii. 2). Still these greater works He did by His Apostles, whereas He includes others besides them, when He says, He that believeth on Me. Are we not to compute any one among the believers in Christ, who does not do greater works than Christ? This sounds harsh if not explained. The Apostle says, To him that believeth on Him that justifieth the ungodly, his faith is counted for righteousness. (Rom. 4:5) By this work then we shall do the works of Christ, the very believing in Christ being the work of Christ, for He worketh this in us, though not without us. Attend then’; He that believeth on Me, the works that I do, shall he do also. First I do them, then he will do them: I do them, that he may do them. Do what works but this, viz. that a man, from being a sinner, become just? which thing Christ worketh in us, though not without us. This in truth I call a greater work to do, than to create the heaven and the earth; for heaven and earth shall pass away, but the salvation and justification of the predestinated shall remain. (c. 3.). However, the Angels in heaven are the work of Christ; shall he who worketh with Christ for his own justification, do greater even than these? Judge any one which be the greater work, to create the just, or to justify the ungodly? At least, if both be of equal power, the latter hath more of mercy. But it is not necessary to understand all the works of Christ, when He says, greater works than these shall he do. These perhaps refers to the works He had done that hour. He had then been instructing them in the faith1. And surely it is a less work to preach righteousness, which He did without us, than to justify the ungodly, which He so does in us, as that we do it ourselves. Great things truly did our Lord promise His people, when He went to His Father: Because I go unto My Father.”