John Calvin Commentary Exodus 2:11

"And it came to pass in those days, when Moses was grown up, that he went out unto his brethren, and looked on their burdens: and he saw an Egyptian smiting a Hebrew, one of his brethren." — Exodus 2:11 (ASV)

And it came to pass in those days, when Moses was grown. Now that faith which the Apostle celebrates began to show itself, when Moses, despising the pleasures and riches of the Court, chose rather to suffer the reproach of Christ than to be considered happy apart from companionship with the chosen people. It was not only love for his nation but also faith in the promises that induced him to undertake this charge, knowing that he would thereby incur the hatred of all the Egyptians. For although he did not immediately resign his wealth, and honorable station, and influence, and power, this was, as it were, the preparation for divesting himself of all these deceitful allurements.

This is why the Apostle says,

He refused to be called the son of Pharaoh’s daughter (Hebrews 11:24).

There is certainly no doubt that he avowed his desire to return to his true and natural kindred, from whom he had been separated. For we gather from the context that he did not come to see his brethren only to pity their condition, but to bring them some consolation and even to share their lot. Nor was the Court so near that he could daily visit them in his ordinary walk. And it is said that he went out the second day.

Therefore, he privately withdrew from the Court or, having asked permission, preferred to expose himself to enmity rather than not reveal his affectionate regard for his people. He relates that he looked on their burdens, or troubles, so that their unjust oppression must have naturally aroused him to give them help. He adds, too, another motive: that he saw an Egyptian smiting an Hebrew.

It is probable that they were harshly treated by their taskmasters if they were slow in their work. Since they were given over to the will of wicked men, it is also probable that anyone could exercise the same cruelty upon them with impunity.