Revach.net: Rav Schwab answers that the gemara in Sanhedrin [98a] says that when the geula comes, if we are zocheh [deserving] Moshiach will arrive on clouds, if not then Moshiach will come come as a pauper on a donkey. Why? The whole world needs to know that Hashem is bringing the geula and Moshiach has no power by himself. If Bnei Yisroel are Maaminim and Ovdei Hashem then Moshiach can come in grand fashion and we will all place thanks in Hashem and not Moshiach. But if we do not recognize Hashem’s hand, then Hashem will need to send a Moshiach who is powerless and destitute to show that it is not his charisma, brains, or money that will release us from the galus.
Moshe was the Goel in Mitzrayim. Bnei Yisroel was not zocheh and Moshe came riding into town on a donkey lacking any pomp or grandeur. He came with the stick in his hand and the shirt on his back. To show his poverty he should have asked Bnei Yisroel to pay for his donkey. Even then he did not, since he did not want to take anything from any member of Klal Yisroel
