Webdog,
My friend, you could not be more wrong with this passage. First off, the structure of this passage shows that God was testing Moses in much the same way He tested Abraham.
Why? Because earlier, in Egypt, before Moses killed the Egyptian slave master, he thought through his might that he would deliver his kinsmen. Acts 7 says:
24 And seeing one of them being wronged, he defended the oppressed man and avenged him by striking down the Egyptian. 25 He [Moses] supposed that his brothers would understand that God was giving them salvation by his hand, but they did not understand.
What God was apparently offering Moses was an unfathomable honor. But, Moses didn't take it. Why? He was more interested in God's glory than his own (quite a change from the old days).
God and Moses both knew that God's promises to Abraham, Isaac, and Jacob cold be fulfilled by God by bringing a new nation from Moses because Moses was an Israelite. So, that's not the issue.
What is the issue is God testing Moses in a way that Moses argues to God that His glory would be diminished, in the eyes of the Egyptians, if He destroyed the people. Also, we see, in Exodus 33, Moses pleading for God Himself to go with the people, again, quite a change in Moses from the old days.
So the point here is the testing of Moses, by God, and we see that Moses has become quite the intercessor for his kinsman rather than trying to set himself up as a the defacto-dictator. No longer is Moses interested in himself, he is interested in performing God's calling on his life to the absolute best of his abilities and he knows, beyond a doubt, that God must be present (physically) if that is to happen.
Moses passed his test with flying colors (yes, only to fail another later), just as Abraham passed his test of sacrificing Isaac.
Also, one of the truths that we see in scripture over and over and over is that God simply does not "Change his mind." Many times when the scripture uses that language it is a simple anthropomorphism. Otherwise, the scripture would contradict itself and, worse yet, God would contradict Himself.
Certainly, as you suggest, there is more than a bit of mystery when it comes to God--what He does and how He does it. But, the scriptures are sufficient, they contain what He wants us to know (not that the scriptures are exhaustive of the knowledge and practice of God). One thing He has stated repeatedly is that He does not change His mind.
Also, there is a biblical order of initiation and response and God is always the initiator and man is always the responder. God acts and man responds. False, pagan religions (such as seen in the episode of Elijah and the prophets of Baal) always, in some way, turn this order up-side-down. The prophets of Baal thought there acts of devotion would entice Baal to respond. This is
not the biblical pattern for worship or dealing with God or His dealings with us.
Blessings,
The Archangel