Or HaChaim on Exodus 3:10/אור החיים על שמות ג׳:י׳

1 לכה ואשלחך, "Go please, and I will send you, etc." Why did G'd say: "I will send you," after He had already told Moses to go? Besides, if anything had to be repeated the sequence should have been the reverse, i.e. "I will send you, go please!" Clearly then G'd wanted that Moses should understand that the actual going to Egypt was not the essence of the mission, only its preamble. Indeed we find later on, after Moses had already gone to Egypt, that G'd instructs him repeatedly to take the Jewish people out of Egypt, i.e. that was the essence of his misssion.

2G'd also used this form of instruction to hint to Moses that one mission would not suffice to take the people out of Egypt but that he would have to perform many errands on behalf of G'd and the people before the Exodus would finally take place. Pharaoh would not agree at once.

3There is another element hinted at in the way G'd instructed Moses. We are taught in Makkot 10 that "G'd leads people on the path they have chosen for themselves." Therefore He first said to Moses: "Go, please!" He meant that if you Moses are willing to perform this commandment, I will send you, i.e. I will fulfil your wish and make you My messenger. From this you learn that if Moses would have refused the mission G'd would not have forced it upon him.

4Perhaps this is the reason that Moses argued with G'd. He did not feel that G'd had commanded him to accept the mission but had left it up to his own volition. Moses felt that G'd had given him leeway and would reply to any reservations he had about accepting such a mission. G'd wanted that when Moses would finally accept the mission he should do so because he wanted to and not because he had been forced to do so.

5You may also take a look at what I have written in connection with Jacob sending Joseph on his fateful mission. G'd may also have assured Moses that if he were concerned about any mishap, he would be a messenger of G'd who had no reason to fear for his safety. In fact this fact saved him in the incident at the inn (Exodus 4,26).