In Parshat Vaera, God requests that Moshe ask Aharon to perform the first three plagues:
Shmot 7:19, God said to Moshe, “Say to Aharon, ‘Take your rod and extend your hand over the waters of Egypt- over the rivers, over their canals, over their lakes, and over every place where their water is gathered, and it (the water) will become blood.’”
Shmot 8:1, God said to Moshe, “Say to Aharon, ‘Extend your hand with your rod over the rivers, over the steams and over the lakes and bring up the frogs upon the land of Egypt.’”
Shmot 8:12, God said to Moshe, “Say to Aharon, ‘Extend your rod and strike the dust of the earth; and it will turn into lice throughout the whole land of Egypt.’”
Why was Aharon asked to perform the plagues of blood, frogs and lice and not Moshe?
In Shmot Raba, Vaera 10:4, Rabbi Tanchum explains that God told Moshe: “The water that saved you when you were put in a basket in the Nile will not be whipped by you.”
In Shmor Raba, Vaera 10:7, Rabbi Tanchum continues: “The dust that protected you when you killed the Egyptian (when you buried the dead body in the sand so that nobody would know) should not be whipped by you.
We learn from here the concept of “Hakarat HaTov”, appreciation for the good that others have done for us, even in the case of water and sand. How much more so should we appreciate the good deeds that other human beings do for us every day which should not be taken for granted.