Why does the Torah mention that a Neveilah renders Tamei whoever touches it both here and later in Pasuk 39?
Rashi (26): The Pasuk is referring to the Neveilah of a Tamei species of animal, whereas the Pasuk later is referring to that of a Tahor species.
Rashi (on Pasuk 6) writes that our Pasuk discusses Neveilah of a Tamei species, and Pasuk 39 discusses Tahor species Why were they taught separately?
Ramban, Rashbam (26), Moshav Zekenim: Our Pasuk does not mention Misah, for even if it is slaughtered, it has Tum'as Neveilos when it dies. Pasuk 39 mentions Misah, to indicate that if it is slaughtered, it is not a Neveilah. 1
See Sifsei Chachamim.
Why does the Torah stress "ule'Eileh Titama'u"?
Rashi: The Pasuk refers to the species that are about to be mentioned. 1
Ibn Ezra: It refers to the species mentioned above. 2 .
Moshav Zekenim: However, fish, birds and locusts mentioned above do not have Tum'as Neveilos.
I.e. also fish, birds and locusts have Tum'as Neveilos. The Ramban says that the Ibn Ezra erred. (I.e. even based on Ibn Ezra's style, to ignore Midrashei Chazal and explain according to the simple meaning, since above the Torah mentioned Tum'ah only regarding animals, and Sheketz regarding fish, birds and Sheretz ha'Of, surely only animals have Tum'ah! - PF)
What are the ramifications of the fact that one becomes Tamei?
Rashi (on Pasuk 29): A Tamei person is forbidden to eat Terumah and Kodshim, and to enter the Beis-ha'Mikdash.
How does the Tum'ah go away in the evening?
Here, the Torah permits becoming Tamei through a Neveilah. Above (Pasuk 8), it says "Lo Siga'u"!
Refer to 11:8:3:1-3.