What is the significance of our enemies being so swift?
Ibn Ezra: We could not flee.
Ri Kara: Normally, a pursuer chases enemies that flee to a plain, but if they flee to a mountain, he despairs of chasing, lest he weary on the mountain. These chased us also on mountains!
Palgei Mayim: This was in order to bring the Galus early, amidst Chesed (refer to 4:18:2:2).
What is the meaning of "[Al he'Harim] Delakunu"?
Ibn Ezra, Rid: This is [chased], like "Ki Dalakta Acharai" (Bereishis 31:36).
Refer to 4:19:1:2.
Palgei Mayim: In the merit of the Avos, who are called Harim, they chased us quickly to bring the Galus early, lest "v'Noshantem
What is the significance of ambushing in the Midbar?
Ri Kara: Normally, a pursuer chases in settled places, but if enemies flee to a Midbar, he ceases chasing. These ambushed us also in the Midbar!
Palgei Mayim: It was due to Chet ha'Egel in the Midbar.