Frank Sheed was blessed with a genius for explaining the mysterious with clarity. St. Augustine's manifold genius included a talent for inquiring into the mysterious with power and beauty. From St. Augustine's "On the Trinity" (full text
here):
Let us now inquire more carefully, so far as God grants, into that which a little before we deferred; whether each person also in the Trinity can also by Himself and not with the other two be called God, or great, or wise, or true, or omnipotent, or just, or anything else that can be said of God, not relatively, but absolutely; or whether these things cannot be said except when the Trinity is understood. For the question is raised—because it is written, “Christ the power of God, and the wisdom of God,” — whether He is so the Father of His own wisdom and His own power, as that He is wise with that wisdom which He begot, and powerful with that power which He begot; and whether, since He is always powerful and wise, He always begot power and wisdom. For if it be so, then, as we have said, why is He not also the Father of His own greatness by which He is great, and of His own goodness by which He is good, and of His own justice by which He is just, and whatever else there is? Or if all these things are understood, although under more names than one, to be in the same wisdom and power, so that that is greatness which is power, that is goodness which is wisdom, and that again is wisdom which is power, as we have already argued; then let us remember, that when I mention any one of these, I am to be taken as if I mentioned all. It is asked, then, whether the Father also by Himself is wise, and is Himself His own wisdom itself; or whether He is wise in the same way as He speaks. For He speaks by the Word which He begot, not by the word which is uttered, and sounds, and passes away, but by the Word which was with God, and the Word was God, and all things were made by Him: by the Word which is equal to Himself, by whom He always and unchangeably utters Himself. For He is not Himself the Word, as He is not the Son nor the image. But in speaking (putting aside those words of God in time which are produced in the creature, for they sound and pass away—in speaking then) by that co-eternal Word, He is not understood singly, but with that Word itself, without whom certainly He does not speak. Is He then in such way wise as He is one who speaks, so as to be in such way wisdom, as He is the Word, and so that to be the Word is to be wisdom, that is, also to be power, so that power and wisdom and the Word may be the same, and be so called relatively as the Son and the image: and that the Father is not singly powerful or wise, but together with the power and wisdom itself which He begot (genuit); just as He is not singly one who speaks, but by that Word and together with that Word which He begot; and in like way great by that and together with that greatness, which He begot? And if He is not great by one thing, and God by another, but great by that whereby He is God, because it is not one thing to Him to be great and another to be God; it follows that neither is He God singly, but by that and together with that deity (deitas) which He begot; so that the Son is the deity of the Father, as He is the wisdom and power of the Father, and as He is the Word and image of the Father. And because it is not one thing to Him to be, another to be God, the Son is also the essence of the Father, as He is His Word and image. And hence also— except that He is the Father [the Unbegotten]— the Father is not anything unless because He has the Son; so that not only that which is meant by Father (which it is manifest He is not called relatively to Himself but to the Son, and therefore is the Father because He has the Son), but that which He is in respect to His own substance is so called, because He begot His own essence. For as He is great, only with that greatness which He begot, so also He is, only with that essence which He begot; because it is not one thing to Him to be, and another to be great. Is He therefore the Father of His own essence, in the same way as He is the Father of His own greatness, as He is the Father of His own power and wisdom? Since His greatness is the same as His power, and His essence the same as His greatness.