Chazal say: לְעולָם יַעֲסֹק אָדָם בַתורָה וּבַמִצְוות אֲפִלוּ שֶלֹא לִשְמָהּ שֶמִתוךְ שֶלֹא לִשְ מָהּ בָא לִשְמָהּ פסחים נ ב A person needs to start off learning Shelo Li'shmah. You must first have Shelo Li'shmah (selfish reasons) and mix your Yetzer into your holy Avoda. However, eventually you have to become total Li'shmah and Ruchani. Therefore, we continuously “trade” a Treife: חֲמור donkey for a kosher: שֶה sheep. Like the Chovos Halvavos says we need to “trade” our love for Olam HaZeh for a love for Ruchaniyus. We need the: חֲמור donkey as a stepping stone, but ultimately, we need to focus more and more on Ruchaniyus.
Our eating the Korban Pesach in a happy joyous family setting can symbolize why it was worth the trade from Gashmiyus to Ruchaniyus, since the Korban Pesach was a kosher, obedient sheep, and Chazal say that Hashem made it smell like Gan Eden. Leaving Mitzrayim means leaving fake Gashmiyus pleasure for real Ruchaniyus pleasure. For good reason Moshe kept saying: “We have to leave כִי חַג ה' לָנוּ י ט because we have a holiday” ...
