Ineffability is just one of the magic words in the theist's Toolbox of Cheating:
"Don't give me logic, it doesn't count because your reason is invalid because God."
So how do you 'know' he's ineffable, eh? Oh yeah, because you said so and your mind is just as feeble as mine.
"Because he is God, who is by definition all the things I want him to be".
Circular logic, another favourite.
You'll be coming at me with transubstantiation next.