en_tn/num/19/12.md

purify himself

The person would ask someone who is clean to purify him by sprinkling on him some water mixed with the cows ashes. Asking someone to purify him is spoken of as if he were to purify himself. Alternate translation: "ask someone to purify him" (See: rc://en/ta/man/jit/figs-metonymy)

if he does not purify himself the third day, then he will not be clean on the seventh day

This can be stated in a positive form. Alternate translation: "he will be clean on the seventh day only if he purifies himself the third day" (See: rc://en/ta/man/jit/figs-doublenegatives)