He shall purify himself with it on the third day and on the seventh day he shall be clean; but if he does not purify himself on the third day and on the seventh day, he shall not be clean.
Torah Temimah: Kiddushin 62a — Rabbi Meir says: Any condition that is not like the condition of the sons of Gad and the sons of Reuven is not a [valid] condition. And this is what is written: “he shall purify himself with it… he shall be clean; and if he does not purify himself… he shall not be clean.”
English: Rabbi Meir says: Any condition that is not like the condition of the sons of Gad and the sons of Reuven is not a [valid] condition. And this is what is written: “he shall purify himself with it… he shall be clean; and if he does not purify himself… he shall not be clean.”
Model for a complete dual-sided condition (both positive and negative).
A valid condition in Jewish law must state both the positive and the negative outcomes, modeled on the language of this verse and the classic condition of the tribes of Gad and Reuven.