Why does the Torah insert the (otherwise superfluous) word "u'va'Yom"?
Sifra: To preclude the Zav from bringing his Korban on the eighth night. 1
See Torah Temimah, note 56.
Why does the Torah insert the (otherwise superfluous) word "Yikach Lo"?
Sifra: To teach us that the Zav must designate the birds specifically for that Zivus, and not use birds that he designated for a previous Zivus.
Why does the Torah insert the (otherwise superfluous) words "u'Ba Lifnei Hashem ... "?
Nazir, 44b: To teach us that the Zav must prepare himself to come before Hashem, by Toveling on the seventh day before nightfall, in order not to be a T'vul-Yom when he comes to bring his Korban.
