1 Samuel 27:6 - Joseph Benson’s Commentary on the Old and New Testaments

Achish gave him Ziklag Not only that he might inhabit it for the present, but possess it as his own in future. This Achish did, either out of his royal bounty, or on condition of some service which David was to perform. Or perhaps he thought hereby to lay the greater obligations on David, whom he knew to be so able to serve him. In the division of the country it was first given to the tribe of Judah, Joshua 15:31; and afterward to that of Simeon, who had a portion out of the land given to Judah, Joshua 19:5. But the Philistines kept possession of it, so that neither of them enjoyed it, till now, by the gift of Achish, it became the peculiar inheritance of David and his successors. Ziklag pertaineth unto the kings of Judah unto this day This and such clauses were evidently added after the substance of the books in which they are contained was written.