1 Corinthians 2:6-7
3 And though it be everywhere preached, still is it a mystery; for as we have been commanded, “what things we have heard in the ear, to speak upon the house tops,” so have we been also charged, “not to give the holy things unto dogs nor yet to cast our pearls before swine.” For some are carnal and do not understand: others have a veil upon their hearts and do not see: wherefore that is above all things a mystery, which everywhere is preached, but is not known of those who have not a right mind; and is revealed not by wisdom but by the Holy Ghost, so far as is possible for us to receive it. And for this cause a man would not err, who in this respect also should entitle it a mystery, the utterance whereof is forbidden. (ἀπόῤῥητον) For not even unto us, the faithful, has been committed entire certainty and exactness. Wherefore Paul also said, “We know in part, and we prophesy in part: for now we see in a mirror darkly; but then face to face.”
4. For this cause he says, “We speak wisdom in a mystery, the hidden wisdom which God fore-ordained before the worlds unto our glory. Hidden:” that is, that no one of the powers above has learned it before us; neither do the many know it now.
“Which he fore-ordained unto our glory” and yet, elsewhere he says, “unto his own glory,” for he considers our salvation to be His own glory: even as also He calls it His own riches, though He be Himself rich in good and need nothing in order that He may be rich.
“Fore-ordained,” he says, pointing out the care had of us. For so those are accounted most both to honor and to love us, whosoever shall have laid themselves out to do us good from the very beginning: which indeed is what fathers do in the case of children. For although they give not their goods until afterwards, yet at first and from the beginning they had predetermined this. And this is what Paul is earnest to point out now; that God always loved us even from the beginning and when as yet we were not. For unless He had loved us, He would not have fore-ordained our riches. Consider not then the enmity which has come between; for more ancient than that was the friendship.
As to the words, “before the worlds,” (πρὸ τῶν αἰώνων) they mean eternal. For in another place also He says thus, “Who is before the worlds.” The Son also, if you mark it, will be found to be eternal in the same sense. For concerning Him he says, “By Him He made the worlds;” which is equivalent to subsistence before the worlds; for it is plain that the maker is before the things which are made.
Source: Homilies on First Corinthians (New Advent)