I have probably not been coherent here, because I understand your point, but it doesn't appear we are on the same page. God is not accepting a challenge so much as answering it, to illustrate..
If you were to challenge adamantly that gravity had no hold on you, and that you could fly out the window, and you did not trust my word enough not to jump, you would excuse me the act of placing a safety net beneath the window in question. Am I insincere in accepting a challenge? by allowing you to jump, all the while ensuring that you do not need to see harm, I am not accepting a challenge at all, but answering it. I am pretty sure you will learn in the best way possible that you were wrong and there would be no need for you or anyone else watching to jump out any windows.
So, ambitious man has challenged his God, God has to answer that challenge, words would do no good as his words had been brought into question as part of the challenge, so the answer has been made through what has thus far amounted to 6000 years of experimentation in many different kinds of rulership (opinions over success may differ) By then contrasting this in full view with his own government for 1000 years, Gods sincerity in the matter is in answering the challenge.
I apologise if I sound bonkers, I appreciate how us theists must sound at times to those of you who do not share in our psychological shortcomings