Rashi and Targum Yonasan: It implies that whatever Hashem declared an abomination - such as a B'chor the ear of which the owner nicked in order to Shecht and eat outside Yerushalayim - the Torah prohibits Shechting and eating, ¹ and meat and milk that are cooked together, the Torah prohibits eating (and from deriving benfit - as implied by "Lo Sochl" - Chulin, 114b, citing R. Avahu).

Ramban and Seforno: It applies to all the Tamei species of animals ² (which are abhorrent ³ to the soul which is pure - Ramban). ⁴

Avodah Zarah, 66a: It implies that whatever the Torah forbade to eat is considered like one La'av and that consequently, all forbidden species combine with each other to make up the required Shi'ur. ⁵

Oznayim la'Torah: Bearing in mind that the majority of animals are forbidden, ⁶ the Torah presents the Din regarding the majority of animals, before it lists the ten Kasher ones; By the same token, in Pasuk 11, it writes "Kol Tzipor Tehorah Tocheilu" regarding the majority of Tahor birds, before listing the twenty-four Tamei ones. ⁷

Rashi (on Pasuk 7): The animals are repeated on account of the Shesu'ah (in Pasuk 6) and the birds because of the Ra'ah (in Pasuk 13) which it did not list in Shemini. ¹

Ramban: Because all the items mentioned here fall under the category of 'To'evah', ¹ in which case it is not necessary to mention Sheratzim, since everybody knows that they are abominable. ²

Ramban: Refer to 14:3:3:1. And a T'reifah animal is forbidden (not because it is abominable, but) because of the poison in its body or the sickness that it has contracted, both of which are potentially fatal to humans.

Moshav Zekenim: Because, since the Torah prohibits offering them on the Mizbe'ach, it implies that people may eat them. ¹