וצוה הכהן ולקח למטהר שתי צפרים…(מצורע יד:ד)

According to the phrase’s grammar, the word “למטהר” should’ve been written with the letter “נ” – “לנטהר” in the current tense- since the ‘metzora’ (impure) is currently getting cleansed.  (The word “מטהר” personifies one that cleans the other.) Teaching us that it’s not enough for the metzora to depend on the Kohen to cleanse him. The inflicted person has to contribute to the cleansing by doing teshuvah.  Therefore, it says “למטהר” – the one that cleanses, since the metzora himself does the primary cleansing.