11 What follows? “Once has God spoken, these two things I have heard, that power is of God, and to You, O Lord, is mercy, for You shall render to each one after his works”....“Once has God spoken.” What do you say, Idithun? If you that had leapt over them art saying, “Once He has spoken;” I turn to another Scripture and it says to me, “In many quarters and in many ways formerly God has spoken to the fathers in the prophets.” What is, “Once has God spoken”? Is He not the God that in the beginning of mankind spoke to Adam? Did not the Selfsame speak to Cain, to Noe, to Abraham, to Isaac, to Jacob, to all the Prophets, and to Moses? One man Moses was, and how often to him spoke God? Behold even to one man, not once but ofttimes God has spoken. Secondly, He has spoken to the Son when standing here, “You are My beloved Son.” God has spoken to the Apostles, He has spoken to all the Saints, even though not with voice sounding through the cloud, nevertheless in the heart where He is Himself Teacher. What is therefore, “Once has God spoken”? Much has that man leapt over in order to arrive at that place, where once God has spoken. Behold briefly I have spoken to your Love. Here among men, to men ofttimes, in many ways, in many quarters, through creatures of many forms God has spoken: by Himself once God has spoken, because One Word God has begotten....For it could not be but that God did Himself know that which by the Word He made: but if that which He made He knew, in Him there was that which was made before it was made. For if in Him was not that which was made before it was made, how knew He that which He made? For you can not say that God made things He knew not. God therefore has known that which He has made. And how knew He before He made, if there cannot be known any but things made? But by things made there cannot be known any but things previously made, by you, to wit, who art a man made in a lower place, and set in a lower place: but before that all these things were made, they were known by Him by whom they were made, and that which He knew He made. Therefore in that Word by which He made all things, before that they were made, were all things; and after they have been made there are all things; but in one way here, in another there, in one way in their own nature wherein they have been made, in another in the art by which they have been made. Who could explain this? We may endeavour: go ye with Idithun, and see.
12....For even the Lord says, “Many things I have to say to you, but you cannot bear them now.” What is therefore, “These two things I have heard”? These two things which to you I am about to say not of myself to you I say, but what things I have heard I say. “Once has God spoken:” One Word has He, the Only-begotten God. In that Word are all things, because by the Word were made all things. One Word has He, “in whom all the treasures of wisdom and knowledge are hidden.” One Word He has, “once has God spoken.” “These two things,” which to you I am about to say, these I have heard: not of myself I speak, not of myself I say: to this belongs the “I have heard.” But the friend of the Bridegroom stands and hears Him, that he may speak the truth. For he hears Him, lest by speaking a lie, of his own he should speak: lest you should say, Who are you that sayest this thing to me? Whence do you say this to me? I have heard these two things, and I that speak to you that I have heard these two things, am one who also does know that once God has spoken. Do not despise a hearer saying to you certain two things for you so necessary; him, I say, that by leaping over the whole creation has attained unto the Only-begotten Word of God, where he has learned that “once God has spoken.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)