6 And as if to point out the cause why they are enemies of God's people, he adds, “For Assur came with them.” Now Assur is often used figuratively for the devil, “who works in the children of disobedience,” as in his own vessels, that they may assail the people of God. “They have helped the children of Lot,” he says: for all enemies, by the working in them of the devil, their prince, “have helped the children of Lot,” who is explained to mean “one declining.” But the apostate angels are well explained as the children of declension, for by declining from truth they swerved to become followers of the devil. These are they of whom the Apostle speaks: “You wrestle not against flesh and blood, but against principalities and powers, and the rulers of the darkness of this world, against spiritual wickedness in high places.” Those invisible enemies are helped then by unbelieving men, in whom they work in order to assail the people of God.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)