John Calvin Commentary Psalms 135:10

"Who smote many nations, And slew mighty kings," — Psalms 135:10 (ASV)

He smote great nations. He now comes to speak of the purpose for which God delivered them from their bondage. He did not lead His people out of Egypt and then leave them to wander as they pleased, but brought them out so that He might settle them in the promised inheritance.

The Psalmist mentions this as another significant proof of God's favor and His unwearied kindness to them; for having once taken the children of Abraham by the hand, He led them on, in the continued exercise of His power, until He put them in possession of the promised land.

He takes the opportunity to extol God’s power from the fact that it was only after the slaughter of many enemies that they came to the peaceable possession of the country. And it was a striking illustration of divine goodness to show this preference for the Israelites, who were merely a multitude of insignificant people, while those opposed to them were mighty kings and powerful nations.

Notice is taken of two kings, Sihon and Og, not because they were more powerful than the rest, but because, by blocking the entrance to the land before them, they were the first formidable enemies encountered. Besides, the people were not yet accustomed to war. As the crowning act of the Lord’s goodness, the Psalmist adds that the Israelites obtained firm possession of the land.

Someone has said—

“Non minor est virtus quam quaerere, parta tueri,”

“It is no less an achievement to keep possession than to acquire it;” and since the Israelites were surrounded by deadly enemies, the power of God was very prominently displayed in preserving them from being rooted out and expelled again—an event that would have repeatedly taken place had they not been firmly settled in the inheritance.