Pesach is called Zman Cheiruseinu (Time of our Freedom) presumably because we were freed from being slaves of Pharaoh. But, the Jewish nation is NOT halachically free to do whatever it pleases. We are still slaves of Hashem, as we say in Shacharis during Berich Shmei, "Anno Avda DeKudsha Brich Hu" (I am the slave of The Holy One Blessed be He).
I heard in a shiur that Pesach is the Yom Tov celebrating our transfer of being slaves of Paraoh to being slaves of HaShem.
Primarily looking for answers/solutions from Rishonim and earlier (e.g. Chazal).