Here taking a page from the Trinitarian book.
The Oneness of God is a mystery beyond the comprehension of men and must be accepted by faith.
the finite creature, man, could never fully comprehend the nature, inner workings and thoughts of his infinite Creator. The much higher form of divine existence is mysterious to the lower form of human existence. If we cannot fully understand our own being, how can we comprehend fully the mystery of our Creator! Man's knowledge is restricted by the mode of his learning, which takes place through finite reality in this life.
If they can say it like that, why can't we?