What does "Yafli Neder" mean?
Rashi, Rashbam, Targum Onkelos and Targum Yonasan: It means that one verbally expresses a Neder. 1
Rashbam: Specifying exactly what the Neder is all about.
What is the definition of 'Erech'?
Rashi (in Pasuk 3): It is a fixed value 1 that the Torah gives to a person depending on a combination of age (and sex).
Rashi: Which has no connection with the person's market value.
Why does the Torah add a second 'Chaf'.
Rashi: Does not know the reason for the extra 'Chaf'.
Rashbam: The Torah sometimes doubles letters. 1
Torah Temimah (citing Erchin, 4b): It comes to include there where someone declares 'Erech S'tam alai' without specifying, to teach us that he is Chayav to pay Hekdesh the least of the Erchin. 2
If this Parshah was said at Har Sinai - as the Torah testifies in Pasuk 34, why did the Torah not insert it B'har?
Ramban: Because, although some of the Pesukim are connected to the Yovel, 1 the Torah prefers to discuss all the Dinim of Neder together.
Seforno: Refer to 26:46:1:1*.
Ramban: Such as those that deal with the sanctification of fields that one purchases and that one inherits,
Why does the Torah insert the word "Nefashos"?
Rashi: To include a casee where a person declares the Erech, not of a whole person, but of a major limb, without which the person cannot live.