The Torah calls Pesach "Chag Hamatzot." But we call it "Pesach." Why is this so? Rabbi Chaim of Volozhin explains as follows:
The word Matzot and the word Mitzvot are spelled exactly the same in Hebrew. Thus "Chag HaMatzot" can be read "Chag HaMitzvos," meaning that by leaving Egypt and receiving the Torah, the Jewish People now have the opportunity to earn great reward by doing the Mitzvot.
Pesach, on the other hand, means Passover: God "passed over" the houses of the Jewish People. By calling it Pesach, we emphasize the good that God has done for us.
Our Sages teach us not to serve God with an eye to the reward; rather we should serve Him out of a sense of love and gratitude. By calling it Pesach we de-emphasize the reward that each Mitzva brings, and instead focus on the good that God does for us.