If, like Mohammad, you decided to make up a religion for profit, power and gain, you wouldn't come up with the Trinity. Three Persons, one God isn't the kind a thing a huckster would pitch to his mug punters, it's too difficult. And therein lies one of the arguments for the revealed truth of Christianity. That said, how can we make sense of it? Frank Sheed, in Theology and Sanity, explains Thomas Aquinas' reasoning with clarity.
Starting from the infinite knowledge of God, Sheed makes the point that such knowledge must have a commensurate object that is also infinite. God's knowledge must therefore be self-knowledge and this concept or idea is the Son or Word. He advises the "beginner" to study the following "minutely":
An idea is, so far as we can make it so, the mental double or image of the object we are contemplating; it expresses as much of that object as we can manage to get into it. Because of the limitation of our powers, the idea we form is never the perfect double or image, never totally expresses the object, in plain words is never totally adequate. But if God does, as we know from Himself that He does, generate an idea of Himself, this idea must be totally adequate, in no way less than the Being of which it is the Idea, lacking nothing that that Being has.
The Idea must contain all the perfection of the Being of which it is the Idea. There can be nothing in the Thinker that is not in His Thought of Himself, otherwise the Thinker would be thinking of Himself inadequately, which is impossible for the Infinite.
Thus the Idea, the Word that God generates, is Infinite, Eternal, Living, a Person, equal in all things to Him Who generates It. Someone as He is, conscious of Himself as He is, God as He is.
So we see the Son, begotten from the infinite knowledge of the Father and as with knowledge, likewise with love. Father and Son combine in an infinite act of love which produces a perfect state of "Lovingness" which has all that they have.
To a point the two "processions" are parallel. The First Person knows Himself; His act of knowing Himself produces an Idea, a Word; and this Idea, this Word, the perfect Image of Himself, is the Second Person. The First Person and the Second combine in an act of love of one another, love of the glory of the Godhead which is their own; and just as the act of knowing produces an Idea within the Divine Nature, the act of loving produces a state of Lovingness within the Divine Nature.
Into this Lovingness, Father and Son pour all that They have and all that They are, with no diminution, nothing held back. Thus this Lovingness within the Godhead is utterly equal to the Father and the Son, for They have poured Their all into it. There is nothing They have which Their Lovingness does not have. Thus Their Lovingness too is Infinite, Eternal, Living, Someone, a Person, God.
Observe that here again we are still within the Divine Nature. For love is wholly within the nature of the lover.
But this love wholly contains the divine Nature, because God puts the whole of Himself into love.
Complicated? No, it's not so much that as so simple it's not easy, but whoever said life would be? Thank you, Frank Sheed, for explaining the Angelic Doctor so clearly.
You can read the whole thing here.
God bless,
LSP
