As part of the preparations for departure from Egypt, Israel were called upon to perform actions that would symbolise the change in their physical fortunes from bondage to freedom, as well as their spiritual transformation from cultural and religious enslavement to acceptance of the true G-d.
Nechama Leibowitz discusses the Israelites’ tethering of the lamb(sacred to the Egyptians) outside their houses, 4 days before its slaughter. She quotes Rashi who explained that they should take the lamb, then ensure that all the males were circumcised in time to have three days to recover and then be ready for the departure from Egypt after eating the sacrificed and roasted lamb. He took the expression “you were naked and bare” to mean that the Israelites up to that time had no Mitzvot to follow, and therefore no merit to justify their redemption. The ritual with the lamb distinguished the Jews from the Egyptians.
Another difference between this and subsequent celebrations of Pesach was the command to dip a bunch of hyssop in the blood of the lamb and spread it on the lintel and doorposts of the house. Rambam’s commentary was that this action was to publicly demonstrate the rejection of the Egyptian idolatry, and the protection from retribution. What had previously been dangerous now became the source of deliverance. The commandment would have brought about a change in outlook, liberation from Egyptian superstition and release from the fear of their Egyptian taskmasters.
Nechama Leibowitz concludes that the practical act of redemption was accompanied by in depth changes in mentality. She also quotes from R’ SR Hirsch who argued that the family within the home was the focus for the ritual. There was one lamb for each family who had to eat within walls and behind a door with the blood on the posts and the lintel.
The home provided the social insulation vis-à-vis society, and physical insulation against the forces of nature. That night there was not an Egyptian house which did not have a corpse, but the Israelite houses were spared. The strength of the Jewish people came from the families, nurturing the individual members.
Acceptance of G-d’s Mitzvot came with freedom, from the celebration of the new month, the calculation of the calendar from the month of deliverance, the rules of subsequent Seder meals, during the festival of Pesach, redemption of the firstborn, and the wearing of Tefillin.