The sources and reasons behind Shlissel Challah
The custom some women (or men) have of baking the house key into the challah on the Shabbat following Pesach (also known as a shlissel [=key] challah) is explained with the following reasons: Based on “Pitchi Li Achoti, Ra’ayati…” (“Open up, my darling…” — Shir HaShirim 5:2), on which the Midrash states “Pitchu li petach ke-chudo shel machat…,” (cf. Shir HaShirim Rabbah 5, s.v. “Kol Dodi Dofek“) = something like “Open your hearts (in teshuvah) like the eye of the needle, and I (God) will open the rest like [a very large opening]. According to Kabbalah on Pesach the gates to heaven were open, and following Pesach the lower gates are shut, and it’s up to us to open them again, therefore on the first Shabbat we put the key on the challah to show that through the mitzvah of Shabbat we are opening the locks [original source?]. In the desert the Jewish people ate from the manna until after Pesach upon entering the land (with the bringing of the Omer, see: Josh. 5:11), at which poin...