Moshe complains about the accusations hurled against him and says "Lo Chamor Echad Meihem Nasasi" - I didn't even take a single donkey from them [Korach 16:15]. Rashi says this refers to when he came down to Mitzrayim to redeem them on a donkey, and he paid for it from his own money. Rav Shimon Schwab asks, why would Moshe think that he should have taken the money from Bnei Yisroel.
Rav Schwab answers that the gemara in Sanhedrin [98a] says that when the geula comes, if we are zocheh [if we merit it] 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 [believers] and Ovdei Hashem [servants of 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.