What is the word "Zos" coming to preclude?
Sifra. It comes to precludes a Zav who urinates from the need to re-count one day. 1
What are the connotations of "Zos Toras ha'Zav ... "?
Targum Yonasan: The Torah is warning us to treat the Tum'os under discussion with care and to bring the prescribed Korbanos upon becoming Tahor, in order to attain atonement.
Nedarim, 35b: It teaches us that a Zav Katan has the same Din as a Zav Gadol, 1 inasmuch as one can bring a Korban on his behalf, since the Korban of a Zav 2 is not brouht as a Kaparah, but to permit him to eat Kodshim and to enter the Beis-Hamikdash, and does not therefore require Da'as.
Nidah, 34b: It teaches us that a Zav Katan has the same Din as a Zav Gadol, inasmuch as the first sighting of Zivus renders him Tamei. 3
Why does the Torah mention a Zav twice, once in this Pasuk and once in the next?
Rashi: In this Pasuk, it is referring to a Zav after his first sighting, whereas in the next Pasuk it is referring to a Zav who had two or three sightings.
Seforno: Once, to clarify that, since the Zav requires a Korban, it is a sign that he sinned, and once, to distinguish between a Zav and a Zavah.
Why does the Torah juxtapose Ba'al-Keri to a Zav who has had one sighting?
Rashi: To teach us that the first sighting of a Zivah is Metamei until nightfall - like a Ba'al Keri.
Seforno: To teach us that, like a Zav, a Ba'al Keri sinned - by virtue of the fact that his emission inevitably ocurred as a result of sinful thoughts, 1 due to the sin of the Eitz ha'Da'as, which came about through the snake, and not in order to have children.
Megilah, 20a: To teach us that a Zav may Tovel in the day, like a Ba'al Keri, 2
Nidah, 35a: To teach us that the first sighting of a Zav is Metamei be'Oneis 3
