During each of the first three makos, we are taught a critical lesson. Moshe was not permitted to perform the makos of blood and frogs which were brought upon the Nile River. Similarly, the dust of the earth which would turn into lice had to be hit by Aaron rather than Moshe. Chazal teach us that Moshe owed a debt of gratitude to the river and the earth because both had protected him. As a baby, he had been saved by the Nile. After killing the Egyptian who was beating the Jewish slave, Moshe used the dirt to cover the body lest he be discovered. Notwithstanding the significance of expressing gratitude, this seems like a strange place to teach us this lesson. Why are the events of the makos and Yetzias Mitzraim chosen to impart to us the importance of gratitude?
The significance of gratitude permeates the entire story of Yetzias Mitzraim. The introductory pasuk to the decree to enslave the Jewish People speaks about the new Pharoah who did not know Yosef. Whether he literally was a new rule who had never met Yosef or one who "forgot" Yosef, his actions were the ultimate expression of ingratitude to the one who had saved the Egyptian nation. By contrast, Moshe doesn't forget someone who helped him in his time of need. Before returning to Mitzraim to free the Jewish People, he requests permission from Yisro to leave. Yisro had taken Moshe into his home and Moshe never forgot the kindness that had been bestowed on him.
Showing gratitude to other people enables us to develop the trait in ourselves which we ultimately demonstrate towards Hashem. By following the model of Moshe and avoiding the example of Pharoh we can approach our relationship with Hashem in a most proper way. The entire Torah is predicated on the first of the Aseres Hadibros - "I am Hashem Who took you out of Mitzraim." We are eternally grateful for that kindness and it is this gratitude that obligates us to perform His mitzvos. There is no more appropriate place for the Torah to emphasize the lesson of gratitude than at the beginning of the makos which initiated Yetzias Mitzvraim. Moshe taught us to inculcate this character trait in ourselves by expressing gratitude even to inanimate objects such as the river and earth. We continue by being grateful to human beings and culminate by acting in the appropriate manner to Hashem. Our enslavement in Mitzraim and our ultimate deliverance teach us these fundamental lessons about the importance of gratitude in all facets of our lives.
One can only imagine the hypocrisy of Moshe going to take the Jewish People out of Mitzraim thereby instilling in them these feelings for Hashem, yet in the process being ungrateful to Yisro. Specifically at this time, Moshe had to be so careful to even not show ungratefulness to the river and earth. Yetzias Mitzraim had to become the focal point of our expression of gratitude for eternity.