"And they baked unleavened cakes of the dough which they brought forth out of Egypt" (Exodus 12:39). "Cakes": a cake [ugah] is nothing other than a round loaf baked on coals, as in the matter which is said, "knead it, and make cakes" (Genesis 18:6). "Unleavened cakes, for it was not leavened." This teaches that from a kind of dough liable to leaven He brought forth unleavened bread. "Because they were thrust out of Egypt." Because they were thrust out of Egypt, a miracle was done for them, that it should not leaven. "And could not tarry." This teaches that they were not able to delay. "Neither had they prepared for themselves any provisions." This teaches that they took no traveling provisions in their hand.
Unleavened Cakes Baked in Haste When Israel Was Driven Out
Mekhilta DeRabbi Shimon Ben Yochai 12:39
ויאפו את הבצק אשר הוציאו ממצרים עוגות מצות אין עוגה אלא חררה כענין שנאמר (בראשית י"ח ו') לושי ועשי עוגות: עוגות מצות כי לא חמץ. מלמד שממין חמץ הביא מצה: כי גורשו ממצרים. מה שגורשו ממצרים נעשה להן בו נס שלא להחמיץ: ולא יכלו להתמהמה. מלמד שלא יכלו להשתהות: [וגם] צדה לא עשו להם. מלמד שלא נטלו בידם זוודין לדרך: