So the question that came to my mind was "Why?". Why does God get angry merely at rebellion and not at excuses? Why does He poured down wrath on people who who refuse His plan and complain about His goodness? Why doesn't He do the same to those who question their ability to do these thing? Shouldn't we silently and stoically obey all the commands that are given to us, without question? I think the key to all these questions is in Numbers 20.
Numbers 20 is a familiar story as well. Israel has been wondering for several years at this point, having refused to enter the Promised Land when God initially told them to. Thousands of them have died for their rebellion (again, God punishing for outright refusal). And now they are thirsty and without water. In response, God tells Moses to speak to a rock and water will come out for the people to drink. But Moses doesn't speak to the rock; he hits it--twice. And God's response to Moses' rebellion is interesting. He doesn't chide Moses for his anger, his disobedience, or his words. He tells Moses there is punishment coming "because [he] did not believe." His disobedience was founded on unbelief.
God answers our excuses because He understands that our excuses are based on a misunderstanding, or even lack of understanding, of who He is. We don't get it. We don't know His character. So He takes those opportunities to teach us about who He is. Then the choice is ours: to believe or not. If we choose to believe God is who He says He is, then we will obey, trusting His character to accomplish an end we feel is impossible. But if we choose to disobey, we are showing that we really don't believe God is who He says He is. We are calling God a liar. That's why rebellion makes God so angry.
And the moment we fail to believe in God's character, He forbids our entry into the Promised Land. The moment we choose that we are more right than God, He sentences us to years of wandering in a joyless, powerless wilderness. But the moment we believe our God is true, that He cannot lie, that what He says is so, all the peace and riches of the Promised Land are ours to enjoy.