St John of Damascus on the Orthodox Faith Chpt 10

Chapter 10. Concerning divine union and separation.

Therefore all these names must be understood as common to deity as a whole, and as containing the notions of sameness and simplicity and indivisibility and union: while the names Father, Son and Spirit, and causeless and caused, and unbegotten and begotten, and procession contain the idea of separation: for these terms do not explain His essence, but the mutual relationship and manner of existence.

When, then, we have perceived these things and are conducted from these to the divine essence, we do not apprehend the essence itself but only the attributes of the essence: just as we have not apprehended the essence of the soul even when we have learned that it is incorporeal and without magnitude and form: nor again, the essence of the body when we know that it is white or black, but only the attributes of the essence.

Further, the true doctrine teaches that the Deity is simple and has one simple energy, good and energizing in all things, just as the sun's ray, which warms all things and energizes in each in harmony with its natural aptitude and receptive power, having obtained this form of energy from God, its Maker.

But quite distinct is all that pertains to the divine and benignant incarnation of the divine Word. For in that neither the Father nor the Spirit have any part at all, unless so far as regards approval and the working of inexplicable miracles which the God-Word, having become man like us, worked, as unchangeable God and son of God.

St John of Damascus