Is your religion any good if you can understand it? That is a question Garner Ted Armstrong posed many times in TV programs and sermons in addressing the vexed (for some) as to the nature of God. Is God really a mysterious inexplicable, unexplainable three in one, one in three deity? Or is that just a construct of a demented mind? Certainly there is nothing in scripture that points to such a mystery, let alone affirms it.
The booklet “Is God a Mystery” does fully set out the true Biblical explanation of the nature of God.
Also read Mark Armstrong’s article “Blaspheming a Blasphemy”.