John 1:17
“The law was given by Moses, but grace and truth came by Jesus Christ.”
And what means that, says he, “Of His fullness have all we received”? For to this we must for a while direct our discourse. He possesses not, says he, the gift by participation, but is Himself the very Fountain and very Root of all good, very Life, and very Light, and very Truth, not retaining within Himself the riches of His good things, but overflowing with them unto all others, and after the overflowing remaining full, in nothing diminished by supplying others, but streaming ever forth, and imparting to others a share of these blessings, He remains in sameness of perfection. What I possess is by participation, (for I received it from another) and is a small portion of the whole, as it were a poor rain-drop compared with the untold abyss or the boundless sea; or rather not even can this instance fully express what we attempt to say, for if you take a drop from the sea, you have lessened the sea itself, though the diminution be imperceptible. But of that Fountain we cannot say this; how much soever a man draw, It continues undiminished. We therefore must needs proceed to another instance, a weak one also, and not able to establish what we seek, but which guides us better than the former one to the thought now proposed to us.
Let us suppose that there is a fountain of fire; that from that fountain ten thousand lamps are kindled, twice as many, thrice as many, ofttimes as many; does not the fire remain at the same degree of fullness even after its imparting of its virtue to such members? It is plain to every man that it does. Now if in the case of bodies which are made up of parts, and are diminished by abstraction, one has been found of such a nature, that after supplying to others something from itself it sustains no loss, much more will this take place with that incorporeal and uncompounded Power. If in the instance given, that which is communicated is substance and body, is divided yet does not suffer division, when our discourse is concerning an energy, and an energy too of an incorporeal substance, it is much more probable that this will undergo nothing of the sort. And therefore John said, “Of His fullness have all we received,” and joins his own testimony to that of the Baptist; for the expression, “Of his fullness have we all received,” belongs not to the forerunner but to the disciple; and its meaning is something like this: “Think not,” he says, “that we, who long time companied with Him, and partook of His food and table, bear witness through favor,” since even John, who did not even know Him before, who had never even been with Him, but merely saw Him in company with others when he was baptizing cried out, “He was before me,” having from that source received all; and all we the twelve, the three hundred, the three thousand, the five thousand, the many myriads of Jews, all the fullness of the faithful who then were, and now are, and hereafter shall be, have “received of His fullness.” What have we received? “grace for grace,” says he. What grace, for what? For the old, the new. For there was a righteousness, and again a righteousness, (“Touching the righteousness which is in the law,” says Paul “blameless.”) There was a faith, there is a faith. (“From faith to faith.”) There was an adoption, there is an adoption. (“To whom pertains the adoption.”) There was a glory, there is a glory. (“For if that which was done away was glorious, much more that which remains is glorious.”) There was a law, and there is a law. (“For the law of the Spirit of life has made me free.”) There was a service, and there is a service. (“To whom pertains the service” and again: “Serving God in the Spirit.”) There was a covenant, and there is a covenant. (“I will make with you a new covenant, not according to the covenant which I made with your fathers.”) There was a sanctification, and there is a sanctification: there was a baptism, and there is a Baptism: there was a sacrifice, and there is a Sacrifice: there was a temple, and there is a temple: there was a circumcision, and there is a circumcision; and so too there was a “grace,” and there is a “grace.” But the words in the first case are used as types, in the second as realities, preserving a sameness of sound, though not of sense. So in patterns and figures, the shape of a man scratched with white lines upon a black ground is called a man as well as that which has received the correct coloring; and in the case of statues, the figure whether formed of gold or of plaster, is alike called a statue, though in the one case as a model, in the other as a reality.
2. Do not then, because the same words are used, suppose that the things are identical, nor yet diverse either; for in that they were models they did not differ from the truth; but in that they merely preserved the outline, they were less than the truth. What is the difference in all these instances? Will you that we take in hand and proceed to examine one or two of the cases mentioned? Thus the rest will be plain to you; and we shall see that the first were lessons for children, the last for high-minded full-grown men; that the first laws were made as for mortals, the latter as for angels.
Source: Homilies on the Gospel of John (New Advent)