What did Moshe mean when he said " ... be'Yad Tishlach!"?
Rashi #1: He meant Aharon, who is accustomed to being sent.
Rashi #2: Rather send someone who will be able to finish the job, since I (Moshe) will not take them into Eretz Yisrael and redeem them in the future. 1
Targum Yonasan: Rather send Pinchas, who (in the guise of Eliyahu ha'Navi) is destined to lead Yisrael in the days of Mashi'ach.
Ramban #1 (citing Targum Onkelos) and Seforno: Why not send someone whose diction is clear, rather than a person with a speech defect, through whose mouth You will have to speak to Pharaoh. 2
Ramban #2: Send anybody other than me, because whoever You send will be a more fitting Shali'ach than me.
Rashbam: Send whoever you want to send, but not me.
Da'as Zekenim: If you want me to go, send with me a letter to advocate for me, for I am not eloquent.
Since Hashem is not short of Sheluchim (Rashi).
As it is not Kavod that Your Shali'ach should be someone whose speech is unclear, seeing as the people will not hear when he speaks with the king, and the fact that a person with such a defect is Hashem's Shali'ach will in itself, be degrading in their eyes (Ramban).
Rashi writes that Moshe knew that he will not take Bnei Yisrael into Eretz Yisrael.In Beha'aloscha (10:29), Rashi says that this was not yet decreed, and Moshe thought that he will enter!
Riva: Moshe knew that he would not lead Bnei Yisrael in, but he thought that he himself will enter.