“Tell the Kohanim descendants of Aharon, and you shall say to them, he may not defile himself in contact with a deceased amongst his people” (21:1).
Our Parsha opens up with the laws that apply exclusively to the Kohen, due to his special spiritual class. The Torah prohibits a Kohen to defile himself with the dead. Apart from prohibiting direct physical contact with the dead there are also many detailed Torah laws that govern the conduction of impurity from the deceased. A most common example is “Tumat Ohel” [the defilement of the tent or house], that if a roof [or tree] overhangs part of the dead corpse, the impurity spreads out to the entire area under the roof. Kohanim must therefore beware of entering a house in which there is a deceased Jewish corpse, and are forbidden to enter a graveyard. Similarly they must keep away from any trees that branch over a grave or corpse. These laws are exclusive to Kohanim, and do not apply to other sectors of the Jewish community.
Rashi notes the double expression with which the Torah informs Kohanim not to defile themselves with the dead: “tell the Kohanim…and you shall say to them”. He quotes to us the Talmud Yevamoth [114a] that quite apart from commanding the Kohanim to keep themselves pure, the Torah is also instructing the Kohanim to say over and warn their young children to keep away from the graveyard and from any contact with the deceased. Although a child is not responsible for his actions until he becomes Bar or Bat Mitzvah, it is the duty of every father to educate his child and regulate him with Torah Study and Mitzvoth. Furthermore the Talmud learns from a combination of verses that we are forbidden to feed or directly propose any Torah prohibition to a Jewish child. The Tur explains that the extra warning and care that is explicitly required by our verse implies that even if we see a little Kohen child innocently heading of his own accord towards having contact with something that may defile him, we are commanded to take the effort and perform our utmost to go and separate him from defilement!
The necessity for the Torah to increase warning and command concerning maintaining the purity of the Kohen stems both from the high spiritual class of the Kohen, and also from the fact that these laws are exclusive to the Kohen. When the Kohen child sees his religious Jewish friends running and playing behind the graveyard and there are overhanging trees, without even thinking he innocently runs and plays together with them – he needs to be specially taught and trained that he is different from them in regards to this issue. The most effective education is by example, and concerning our Mitzvah the training needs to be strong enough to counteract the fact that the Kohen’s very own close friends justly act in a different and permissive manner regarding these laws! It is much harder to discipline against the current and the Torah needs to add a special command to strengthen this education!