Ever try to describe God?
If it is merely a matter of an overwhelmed disbelief, we say He is incredible, unbelievable.
If we merely describe our own reaction of being unable to grasp His nature, we call Him amazing, marvelous, inconceivable.
If we find His nature arresting, we might say He is astonishing or stunning.
If we just label Him with our own estimation of Him, we call Him wonderful, fabulous, marvelous, or awesome.
God transcends our feeble reactions and judgments. His nature lies far above these weak, man-centered attempts to describe Him. He is grand, great, omniscient, omnipresent, immanent, glorious, perfect–
and because human words fail us, ineffable.