Why does it say both "Im Lo Sishme'u" and "v'Im Lo Sasimu Al Lev"?
Malbim: If you will not hear what I warn you, and you will not put to the heart via arousal of the intellect, which obligates honoring My name.
What curse will He send?
Malbim: It is what He said "Arur Nokel" (1:14).
To whom does "Bachem" apply?
Radak: Those who receive [the Korban], and those who bring it.
How will He curse their Brachos?
Rashi: He will curse what needed to be blessed - your grain, wine and oil.
Radak: I blessed you after Binyan ha'Bayis, like it is written. Since you disgrace Me with your Korbanos, I will reverse the Brachah to a curse.
Malbim: You bless the nation with Birkas Kohanim after offering the Korban - "v'Samu Es Shmi Al Bnei Yisrael va'Ani Avarechem" (Bamidbar 6:27) - via you, Hashem blesses the nation. Now you remove My name from Bnei Yisrael, and profane it - I will switch their Brachos to a curse. Also, I already cursed, since you do not put to heart.
Why does it say "v'Gam Arosiha"?
Rashi: Really, you should not attribute the matter to the stipulation that I made "Im Lo Sishme'u", for I knew that they will not hear. Therefore, from now I cursed it.
Radak: Until now I cursed the Brachah that I gave to you, from when you started to disgrace Me via bringing [bad] Korbanos. Now I will increase the curse if you will not listen.
