Why did Moshe read out Seifer ha'Bris to the people?
Seforno: So that Yisrael should know exactly what they are undertaking, in order not to be disillusioned later.
What exactly, does "Na'aseh ve'Nishma" mean?
Rashi (in Shir ha'Shirim, 1:15): 'We will listen, which is synonymous with accepting'.
Rashbam: 'We will do (carry out) what Hashem already said, and we will hear (and carry out) what He will still command us'.
Seforno: 'We will listen with the intention of obeying His instructions'. 1
Targum Onkelos and Targum Yonasan: 'We will do what Hashem says and accept His instructions'.
Hadar Zekenim (8): We will do what He commands us, and we accept the Bris.
What is the significance of the fact that Yisrael declared "Na'aseh" before "Nishma"?
Shabbos, 88a: 'When Yisrael declared "Na'aseh" before "Nishma", 1 a Heavenly Voice announced 'Who revealed this secret to My children
Shabbos )Ibid.): Six undred thousand angels then came and tied two crowns on to the head of eachy person in Yisrael
Why did they first declare "Na'aseh" alone and only now, "Na'aseh ve'Nishma'?
K'li Yakar: Initially, they said "Na'aseh" because they thought that Hashem had aready told them all that He wanted to say. 1 However, when they saw that he sprinkled half the blood on the Mizbe'ach and placed half in the bowls, they wrongly assumed that Hashem was about to add more, and that Moshe would then sprinkle the other half, so they announced "Na'aseh (what He already informed us) ve'Nishma" (what is still to come). 2
What is Seifer ha'Bris?
Rosh: It is the Torah from Bereishis until this point. The one who says that Torah was given Chasumah (only when it was finished, and not each Parshah at a time), this means that it was not written until the end. From Mishpatim and onwards, Moshe received each Parshah orally.