John Calvin on Habakkuk 3:12

The Prophet relates here the entrance of the people into the land of Canaan, that the faithful might know that their fathers would not have obtained so many victories had not God put forth the power and strength of his hand. Hence he says, that God himself had trampled on the land in anger. For how could the Israelites have dared to attack so many nations, who had lately come forth from so miserable a bondage? They had indeed been in the desert for forty years; but they were always trembling and fearful, and we also know that they were weak and feeble. How then was it, that they overcame most powerful kings? that they made war with nations accustomed to war? Doubtless God himself trod down the land in his wrath, and also threshed the nations: as it is said in Psalm 44:5,

“It was not by their own sword that they got the land of Canaan; neither their own power, nor their own hand saved them; but the Lord showed favor to them, and became their Deliverer.”

Justly then does the Prophet ascribe this to God, that he himself walked over the land; for otherwise the Israelites would never have dared to move a foot. Doubtless, they could never have been settled in that land, had not God gone before them. Hence when God did tread on the land in his anger, then it became a quiet habitation to the children of Abraham; warlike nations were then easily and without much trouble conquered by the Israelites, though they were previously very weak.

We now see, that the Prophet sets forth here before the eyes of the people their entrance into the land, that they might know that God did not in vain put to flight so many nations at one time; but that the land of Canaan might be the perpetual inheritance of his chosen people.

The Prophet changes often the tenses of the verbs, inconsistently with the common usage of the Hebrew language; but it must be observed, that he so refers to those histories, as though God were continually carrying on his operations; and as though his presence was to be looked for in adversities, the same as what he had granted formerly to the fathers. Hence the change of tenses does not obscure the sense, but, on the contrary, shows to us the design of the Prophet, and helps us to understand the meaning. It follows at length -

Habakkuk 3:13

13. Thou wentest forth for the salvation of thy people, even for salvation with thine anointed; thou woundedst the head out of the house of the wicked, by discovering the foundation unto the neck. Selah.

13. Egressus es in salutem populi tui, in salutem cum Christo tuo; transfodisti caput e domo impii, nudando fundamentum usque ad collum. Selah.