Why does it say "uv'Chol Zos"?
Rashi: With all this evil that came upon us, we believe and trust in Hashem.
Malbim: Even though we are afflicted, we make a Bris with Hashem - unlike our fathers, who did not serve Him amidst abundance.
What do we write?
Rashi: We write in a Sefer that we accept His kingship on us, so it will be testimony for us.
Ibn Ezra: We will follow the Torah that Hashem gave to Moshe, and not give our daughters to Amei ha'Aretz (30-31).
What is the meaning of "v'Al ha'Chasum"?
Rashi: Most of our great and esteemed people signed on the Sefer of accepting the Mitzvos, to be testimony for us.
Malbim #1: A Sefer on which they signed.
Malbim #2: Everything done to last, they wrote it in two Seforim, one exposed and one Chasum (sealed - Yirmeyah 32:11, 14). They signed inside the exposed Sefer, and on the outside of the Chasum Sefer. This is like Chazal said, a simple Get (document), the witnesses are inside. A tied Get, the witnesses are outside.
In what order did they sign?
Malbim: First the Kohanim signed, and then the Leviyim, and then the Sarim. This was on the revealed Sefer. On the Chasum, they folded the signatures outside, and the order was reversed - first were Sarim, then Leviyim, and then Kohanim.
