John Wesley on 1 Samuel 27:6

Gave Ziklag - Not only to inhabit, but to possess it as his own. Which he did, to lay the greater obligations upon David, whom he knew so able to serve him. It was given to the tribe of Judah before, Josh 15:31, but the Philistines kept the possession of it 'till this time. And being given by them to David, it now belonged not to the tribe of Judah; but to the king of Judah, David and his heirs forever. To this day - This, and some such clauses seem to have been added, after the main substance of the several books was written.