John Calvin on Exodus 15:14-15

14. The people shall hear. Again in this place I have not scrupled to change the tenses; for it is plain that Moses is speaking of things future; although I do not deny, that by verbs of the past tense he confirms the certainty of the matter; which is a common figure with the Prophets. This boast depends on the mention of God’s “strength;” for it was impossible for the Israelites to make their way through so many adverse nations into the land of Canaan, unless God had, as it were, put forth His hand from heaven and fought for them. Lest, then, their numerous difficulties should dishearten them, Moses declares that, although many powerful enemies should endeavor to oppose them, terror shall possess them all from heaven, so that, in their confusion and astonishment, they shall have no power of resistance.