1)
Why does it say "Ba'avur Yishmeru?"?
1.
Radak, Malbim: He gave the land on condition that they guard His Chukim and Toros - "Ki Evi'enu El ha'Adamah Asher Nishbati la'Avosav? v'Hefer Es Brisi 1 ]" (Devarim 31:20). If not, "v'Hayah Le'echol" and they will be exiled from the land. Malbim - this is an introduction to the coming Mizmor, which discusses how they did not guard His Chukim and Toros.
1
Above (Devarim 31:16-17), it says "v'Hefer Es Brisi; ? v'Hayah Le'echol."
2)
Why does it say Hallelukah"?
1.
Radak: The author tells Yisrael in his generation, and their children after them, to praise Hashem for the good that He did with their fathers.
