In the thread about God's grace, Alphus and Omegus emphasized the impossibility of understanding a really ultimate God. I tried to argue there that such a God could still be genuinely understandable to us in part, even if it were only a vanishingly small part. Alphus and Omegus's point shouldn't just be brushed off, though. Even if there is a valid, "Yes, but" to it, as I tried to argue, it's still not going away.
Old religious traditions, like the oldest parts of the Old Testament, don't really seem to make God out (if there even is just one God) to be rational or benevolent. In such old texts I have more a sense of humans trying to deal with God the way pets deal with us: wag the tail if it looks as though food might be offered, otherwise try not to get stepped on. Obey God's commands, the old-time religion seems to say, not because they are admirable moral imperatives issued by a wise and loving being for the good of the universe, but because God is the Big Guy and we don't want to get on his bad side. Life was hard in those days. Humans were all hostages to capricious fate and religion was Stockholm syndrome.
Then after enough centuries humans kind of outgrew that, or something. Our settlements got the City Wall upgrade, life got better, and along with eating better food and sitting on better rugs, we wanted an upgraded God. So we started trying to make out that God was not only big but also good and intelligent, such that we should be obeying God's commands anyway even if God weren't there. A lot of the tail-wagging old tribal piety became embarrassing; if it was still on the books, we tried to give it an acceptable spin.
But maybe that's still pretty naïve theology. Maybe any sufficiently advanced deity, no matter how rational and benevolent, will be indistinguishable to human understanding from a jealous and capricious tribal god who makes arbitrary demands, and rewards and punishes inconsistently.
This is probably the flip side of why humans may need to have faith in a God whom we can't understand. Even if we assume that God really is rational and benevolent, it seems unlikely that God will always seem so to us. So having a more sophisticated faith in a loving and rational God, and having an old-time tail-wagging faith in a capricious tribal god, may not actually be different things. Maybe they're often going to be the same thing, as far as we are concerned.