The Torah commands in (Exodus 12:15), "Seven days shall you eat matzot." But which grains actually qualify for making matzah? The Mekhilta digs into this question with characteristic precision, and the answer shapes Jewish Passover observance to this day.
At first glance, the verse seems open-ended — any grain formed into unleavened bread might count. But a second verse narrows the field dramatically. (Deuteronomy 16:3) instructs, "Do not eat chametz upon it; seven days shall you eat matzot upon it." The key word is "upon it" — the matzah must come from the same material that could become chametz, meaning leavened bread.
This limits the eligible grains to five: wheat, barley, rye, oat, and spelt. These are the grains that, when mixed with water and left to sit, undergo fermentation and rise into chametz. Only something capable of becoming forbidden can be transformed into something that fulfills the commandment.
What about rice, millet, poppyseed, pulse, and sesame? The Mekhilta rules them out explicitly. These substances do not ferment the way the five grains do. They putrefy — they rot and decompose rather than rising. Since they cannot become chametz, they cannot become matzah either.
The ruling reveals a striking principle embedded in Jewish law: the capacity for transgression and the capacity for holiness spring from the same source. The very grains that pose the greatest danger on Passover are the only ones capable of producing its most sacred food.