Think about this for a minute. “Deep down, Moses was not questioning G‑d’s justice, but was just seeking to understand it. Moses and the Jewish people had inherited their faith in G‑d from the patriarchs and matriarchs. This faith was indeed very strong, but in order to be redeemed from Egypt and receive the Torah, it was not enough for their relationship with G‑d to be an inheritance from their ancestors; they had to make it their own. Only when a person internalizes his faith and makes it his own can it permeate his whole being.
Ironically, the way we transform our inherited faith into our own possession is by questioning it – not out of doubt or for the mere sake of questioning, but in order to truly understand it.
Thus, in response to Moses’ desire to understand G‑d’s ways, G‑d told him that the purpose of the exile was to enable the people to reach an even higher level of Divine consciousness than they could by relying solely on their inheritance from the patriarchs.1 Likutei Sichot, vol. 16, p. 51.
Moses took leave of Jethro and set out for Egypt. As G‑d had predicted, when Moses demanded that Pharaoh release the Jews, even for three days, Pharaoh refused. Instead, Pharaoh ordered that the Jews no longer be supplied with straw to make into bricks; they would have to produce the same daily quota of bricks but gather the necessary straw themselves. The Jews complained to Moses; feeling the Jews’ suffering, Moses asked G‑d why He had sent him on this mission if this was the result.
Moses returned to G d and said, “G‑d, why have You mistreated this people?” Exodus 5:22