Why does the Torah repeat the word "Ish"?
Rashi (on Pasuk 25): To include Nochrim in the Din of Nedarim and Nedavos. 1
Menachos, 73b: To bring exclusively Olos
What is the difference between Nedarim and Nedavos?
Rashi and Ramban #2 (citing MIshnah, Kinim, 1:1): Neder is when a person says 'Harei Alai'; Nedavah, when he says 'Harei Zeh'. 1
Ramban #2: A Nedavah is a gift, a Neder, a vow that one makes (to bring an Olah or a Shelamim) when in trouble. 2
Why does the Torah add "le'Chol Nidreihem u'le'Chol Nidosam"?
Ramban: To teach us that even a Nedavah, which one donates when not under duress, 1 must be without a blemish.
Seforno: To disillusion those who think that, since they volunteered to bring the Korban Olah, they are entitled to bring a Ba'al-Mum should they so wish. 2
What is the connection between the previous Parshah and the forthcoming one?
Seforno: The previous Parshah discussed the Dinim of those bringing the Korbanos; the forthcoming Parshah, the equivalent Dinim concerning the Korbanos themselves.