This week’s Parsha begins with Hashem telling Moshe to advise the Kohanim concerning the prohibition of coming into contact with a dead person, ויאמר ה' אל משה אמר אל הכוהנים בני אהרן ואמרת עליהם...
The obvious question is why the Torah, which never wastes a word, repeats itself by saying אמר אל הכוהנים and then again ואמרת עליהם. The Baal Haturim explains that the first אמירה comes to warn the Kohanim that they are forbidden to come into contact with a dead person. The second אמירה advises the Kohanim as to the exceptions to that rule and how they are allowed, even required, to be defiled in a situation of a מת מצוה, where there is no one to care for the deceased and to tend to the body.
Rashi presents the well known answer .להזהיר גדלים על קטנים The Mizrachi, a well known commentator on Rashi, explains that Moshe was to instruct the Kohanim and the Kohanim in turn were to instruct their children. However, if indeed this second telling is for the Kohanim to tell their children, then it should say ואמרתם in the plural form and not ואמרת in the singular. Rav Moshe Feinstein explains Rashi’s comment as follows: when one teaches Torah and Mitzvot, it must be done from two vantage points. The first is to simply teach the details and specifics of the Mitzva, while the second is to teach one to love doing the Mitzvot. Chances of success in the educational effort are much greater when both approaches are taken into consideration and emphasized. Accordingly, we can understand Rav Moshe’s understanding that both אמירות, representing the different emphases involved in the teachings to the Kohanim, were made by Moshe to the Kohanim, who in turn would pass it on to the younger Kohanim.