The festival served as a repudiation of idolatry.
The following article views the biblical celebration of Pesach as a rejection of idolatry. The reader should be aware that the author's reconstruction of the biblical story is based to a great extent on a non-historical reading of the biblical text and draws heavily on the post-biblical midrashic tradition. Reprinted with permission of the publisher from The Jewish Holidays: A Journey Through History (Jason Aronson, Inc).
When the Israelites gathered lambs on the 10th day of the month of Nisan and set them aside for slaughter on the afternoon preceding Passover, they declared themselves free of the influences of the idolatrous practices of the Egyptians. Although the Israelites in Egypt had maintained a distinctive national character during the duration of their enslavement, many, if not most, adopted the idolatrous practices of the Egyptians (Midrash Tanchuma on Exodus 1:7).
The slaughtering of the lamb--considered a deity to the Egyptians--before their oppressors was a public and communal repudiation of idolatry by the Israelites. The Israelites were truly worthy of leaving Egypt only after slaughtering the Passover sacrifice. However, when the Israelites left Egypt, their repudiation of idolatry was not final. The worship of idols would continue to plague the Israelites over the next thousand years until the destruction of the First Temple in 586 BCE.
A New King
During the chaos of the First Temple era, a righteous Judean king prevailed upon the people to desist from their idolatrous practices and mend their ways. This king's emergence and call for change coincided with the approaching Passover holiday. Those changes were characterized by the Passover sacrifices brought by a repentant nation.
Judea had both upright and evil kings. Often the rule of evil kings was followed by the rule of just kings. At the young age of 25, King Hezekiah of Judea inherited a troubled kingdom from his father Ahaz, who had lured the Judeans into idolatry and showed contempt for the holiest site in Judaism--the Temple. Ahaz plundered the Temple of its wealth, brought sacrifices to strange gods, and placed bamot (prohibited altars) throughout the land. (During Temple times, sacrifices were prohibited from being brought outside the Temple walls.)
He also sought the alliance of the powerful Assyrians in the north as protection from Judea's many surrounding enemies. In his desire to mimic the ways of his northern ally, he removed the Temple's copper altar and constructed a likeness of an Assyrian deity in its place. During his rule, Ahaz cancelled the Temple service, prevented the study of the Torah, and permitted immoral practices (Talmud, Sanhedrin 103b).
Immediately upon ascending the throne, Hezekiah sought to right the wrongs of his father. He gathered the Levites and priests and instructed them to purify the Temple. He reminded them of their mission, "My sons, do not forget, for the Lord chose you to stand before Him to minister to Him and to be His ministers and to burn incense (Second Chronicles 29: 11). He also recalled the failures in Judea's history, "…for our fathers acted treacherously and did evil in the eyes of the Lord, our God, and forsook Him, and they turned their faces away from the Tabernacle of the Lord and turned their backs" (Second Chronicles 29:7).