5 “Since they have imagined with one consent; together against You have they disposed a testament”: as though they could be the stronger. In fact, “a testament” is a name given in the Scriptures not only to that which is of no avail till the death of the testators, but every covenant and decree they used to call a testament. For Laban and Jacob made a testament, which was certainly to have force between the living; and such cases without number are read in the words of God.
Then he begins to make mention of the enemies of Christ, under certain proper names of nations; the interpretation of which names sufficiently indicates what he would have to be understood. For by such names are most suitably figured the enemies of the truth. “Idumæans,” for instance, are interpreted either “men of blood,” or “of earth.” “Ismaelites,” are “obedient to themselves,” and therefore not to God, but to themselves. “Moab,” “from the father;” which in a bad sense has no better explanation, than by considering it so connected with the actual history, that Lot, a father, by the illicit intercourse procured by his daughter, begot him; since it was from that very circumstance he was so named. Good, however, was his father, but as “the Law is good if one use it lawfully,” not impurely and unlawfully.
“Hagarens,” proselytes, that is strangers, by which name also are signified, among the enemies of God's people, not those who become citizens, but those who persevere in a foreign and alien mind, and when an opportunity of doing harm occurs, show themselves. “Gebal,” “a vain valley,” that is, humble in pretence. “Amon,” “an unquiet people,” or “a people of sadness.” “Amalech,” “a people licking;” whence elsewhere it is said, “and his enemies shall lick the earth.” The “alien race,” though by their very name in Latin, they sufficiently show themselves to be aliens, and for this cause of course enemies, yet in the Hebrew are called “Philistines,” which is explained, “falling from drink,” as of persons made drunken by worldly luxury.
“Tyre” in Hebrew is called Sor; which whether it be interpreted straitness or tribulation, must be taken in the case of these enemies of God's people in that sense, of which the Apostle speaks, “Tribulation and straitness on every soul of man that does evil.” All these are thus enumerated in the Psalms: “The tabernacles of the Edomites, Ishmaelites, Moab and the Hagarenes, Gebal, and Amon, and Amalech, and the Philistines with those who inhabit Tyre.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)