Not an assumption. A faith thing. But that's just me, in answer to your questions, that have nothing to do with proving God.
However, mankind makes so few cause and effect "chains" where he can determine exactly what the outcome will be...
and the few chains that he does make are so essentially tiny compared with all the cause and effect processes that God has made in the universe...
that it can easily be seen that God is so extremely more complex than mankind, including in intellect...
that when mankind asks about a God-cause...
the answer is so far beyond man and the way he thinks and understands, that...
a microbe would have as much grasp of the answer as a man would.

Okay, so if you're so unsure of why your god does the things that it does, why would you even worship them? Are you SURE that they will allow you into a "heaven" if it does exist at all?
Again, to reiterate, your god is an atheist. Unless you're wrong about your god being eternal.