6 “For aliens have risen up against me”. What “aliens”? Was not David himself a Jew of the tribe of Judah? But the very place Ziph belonged to the tribe of Judah; it was of the Jews. How then “aliens”? Not in city, not in tribe, not in kindred, but in flower....But see the Ziphites, see them for a time flourishing. With reason “alien” sons. You amid the Ziphites hiding said what? “Blessed the people whereof the Lord is its God.” Out of this affection this prayer is being sent forth into the ears of the Lord, when it is said, “for aliens have risen up against me.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)