Why does the Pasuk use the word "Shafal" and not "Amok" (See Rashi) as it did in Pasuk 3?
Ramban (in Pasuk 3): This is because the Nega is not pure white, but white mixed with red, which therefore does not appear as deep as a Baheres on plain skin, which is pure white.
Hadar Zekenim (3), Da'as Zekenim (3): "Shafal" means recessed into the skin. 1
Riva (3): If it discusses the depth of the Nega, it should have omitted "Mar'eha"!
What is the significance of the lengthy statement "v'Tim'o ha'Kohen, Nega Tzara'as Hi"?
Ramban (on Pasuk 3): The Kohen should immediately declare it Tamei, since it is a plague that will definitely turn into Tzara'as.