Or HaChaim on Exodus 5:22/אור החיים על שמות ה׳:כ״ב

1 וישב משה אל השם, Moses returned to G'd, etc. The verse must be understood in this order: "Why did You G'd not tell me at the time when You told me that You would harden Pharaoh's heart that this would involve additional hardship for the people? If You were to answer that the appointed time for relieving the burden of their servitude has not arrived yet, why did You send me already at this time? Moses implied that G'd should have waited with sending him on this mission until the actual slave labour of the Israelites had come to an end.

2We have a reaction by Moses to what G'd had told him previously, namely that the end of the redemption process was not yet at hand but that He, G'd, would advance the time for rescuing the Jewish people by saving them from their oppression. At the end of twelve months the Exodus itself would take place. Moses now asked: "why did You bring harm upon this people?" He meant that if G'd were to tell him that this suffering would advance the redemption, "why did You send me already now? You Yourself have told me that the only reason to commence the mission now was to relieve the people of having to perform slave labour. If as it now appeared, my mission was to be effective only at the time of the Exodus, why did You send me ?" The word זה (numerical value 12) in Moses' question was an allusion to the 12 months the people still had to wait for the redemption. Moses was clearly afraid that Pharaoh's most recent decree would be in effect for the 12 months until the redemption.

3Perhaps Moses also referred to the fact that amongst the Israelites there were those who had to perform slave labour, and others, such as the the tribe of Levi, who were free from that burden. Concerning the former group Moses asked: "why have You brought harm upon them?" Concerning the latter group he asked: "why did You send me on this mission?"

4Moses may also simply have asked: "why did You cause harm to Your people?" G'd's answer would have to be that the harm was the result of Moses' mission. To this Moses retorted: "Why is this (זה) that You have sent me on this mission?" Moses' adding of the word זה was his way of saying that this was why he had been unwilling to undertake the mission in the first place.