What are the implications of the words "Lo Yavo"?
Rashi: To forbid a Kohen even to enter the Ohel in which a Mes is lying.
Why does the Torah insert the word "Nafshos"?
Having just forbidden the Kohen Gadol to render himself Tamei Mes, why does the Torah find it necessary to add "l'Aviv ul'Imo Lo Yitama"?
Rashi: To extrapolate that he may (and should) render himself Tamei for a Mes Mitzvah.
Moshav Zekenim: If he enters Ohel ha'Mes, he transgresses both"Lo Yavo" and "Lo Yitama." A Gezeirah Shavah teaches that the same applies to a Kohen Hedyot.
We learn from "ul'Achoso" written about a Nazir [that he is Metamei for a Mes Mitzvah - Nazir 48b]. Why didn't we learn from a Kohen Gadol? Also here,"l'Aviv ul'Imo" is extra, for it already says that he may not become Tamei for any Mes!
Moshav Zekenim citing R. Hillel: One might have thought that "Al Kol Nafshos Mes Lo Yavo" includes even an animal. We need "l'Aviv ul'Imo" to teach that it applies only to people.
Moshav Zekenim: One might have thought that a Kohen Gadol is not Metamei even for a Mes Mitzvah. Therefore, it says "l'Aviv ul'Imo" he is not Metamei, but he becomes Tamei for a Mes Mitzvah.
QUESTIONS ON RASHI
Rashi writes that he may become Tamei for a Mes Mitzvah. What is considered a Mes Mitzvah?
Da'as Zekenim: The Rambam says that he finds a Mes on the road, and he is so far from people that if he screams, no one will hear. This is a big stringency.