Commentary for Exodus 12:39

עגת מצות means a cake of (made of) unleavened dough (Mekhilta d'Rabbi Yishmael 12:35); dough which has not become leavened is termed וגם צדה לא עשו להם

AND THEY BAKED UNLEAVENED CAKES OF THE DOUGH. The meaning thereof is that they baked unleavened bread of the dough because of the precept which they were commanded: There shall be no leaven found in your homes, for whosoever eateth that which is leavened, that soul shall be cut off from the congregation of Israel.²⁹⁵Above, Verse 19.

כי לא חמץ, it had not had time to rise and ferment due to the short period of time it took to get from Ramses which was still part of Egypt to Sukkot which was already beyond the boundary of Egypt. Our sages in the Haggadah shel Pessach described the experience in the following words: “the dough of our forefathers did not have time to rise and become leavened during the brief time it took for the Lord our G’d to manifest Himself and to redeem them.” The reference of the author of the Haggadah is to the appearance of the pillar of cloud and the pillar of fire as soon as the Israelites had reached Sukkot and left Egyptian soil behind the, This was the manifestation of the Lord G’d of whom he speaks. The Torah there begins to speak of G’d walking in front of the Israelites (Exodus 13,21).