What is this Pasuk coming to teach us?
Rashi: It is coming to add an Asei 1 to the Lo Sa'aseh against eating Tamei species of Sheretz ha'Of.
Ramban #1 (on Pasuk 3): To teach us that all the above-listed birds are abhorrent and that all other species of birds are Tahor and are therefore fit to be eaten by a pure Nefesh.
Ramban #2 (citing R. Shimon in the Sifri): "Kol Of Tahor Socheilu" comes to permit the Tahor species of locust, 2 whereas "ve'Chol Sheretz ha'Of ... " in the previous Pasuk refers to the Tamei species of locust. 3