A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
1 Kings (1 Samuel) 27:1
sa1 27:1SAUL HEARING THAT DAVID WAS FLED TO GATH, SEEKS NO MORE FOR HIM. (Sa1 27:1-4)
David said in his heart, . . . there is nothing better for me than that I should speedily escape into the land of the Philistines--This resolution of David's was, in every respect, wrong: (1) It was removing him from the place where the divine oracle intimated him to remain (Sa1 22:5); (2) It was rushing into the idolatrous land, for driving him into which he had denounced an imprecation on his enemies (Sa1 26:19); (3) It was a withdrawal of his counsel and aid from God's people. It was a movement, however, overruled by Providence to detach him from his country and to let the disasters impending over Saul and his followers be brought on by the Philistines.
1 Kings (1 Samuel) 27:2
sa1 27:2Achish, the son of Maoch, king of Gath--The popular description of this king's family creates a presumption that he was a different king from the reigning sovereign on David's first visit to Gath. Whether David had received a special invitation from him or a mere permission to enter his territories, cannot be determined. It is probable that the former was the case. From the universal notoriety given to the feud between Saul and David, which had now become irreconcilable, it might appear to Achish good policy to harbor him as a guest, and so the better pave the way for the hostile measures against Israel which the Philistines were at this time meditating.
1 Kings (1 Samuel) 27:5
sa1 27:5DAVID BEGS ZIKLAG OF ACHISH. (Sa1 27:5-12)
let them give me a place in some town in the country--It was a prudent arrangement on the part of David; for it would prevent him being an object of jealous suspicion, or of mischievous plots among the Philistines. It would place his followers more beyond the risk of contamination by the idolatries of the court and capital; and it would give him an opportunity of making reprisals on the freebooting tribes that infested the common border of Israel and the Philistines.
1 Kings (1 Samuel) 27:6
sa1 27:6Ziklag--Though originally assigned to Judah (Jos 15:31), and subsequently to Simeon (Jos 19:5), this town had never been possessed by the Israelites. It belonged to the Philistines, who gave it to David.
1 Kings (1 Samuel) 27:8
sa1 27:8David . . . went up, and invaded the Geshurites--(See Jos 13:2).
and the Gezrites--or the Gerizi [GESENIUS], (Jos 12:12), some Arab horde which had once encamped there.
and the Amalekites--Part of the district occupied by them lay on the south of the land of Israel (Jdg 5:14; Jdg 12:15).
1 Kings (1 Samuel) 27:10
sa1 27:10Achish said, Whither have ye made a road to-day?--that is, raid, a hostile excursion for seizing cattle and other booty.
David said, Against the south of Judah, and against the south of the Jerahmeelites--Jerahmeel was the great-grandson of Judah, and his posterity occupied the southern portion of that tribal domain.
the south of the Kenites--the posterity of Jethro, who occupied the south of Judah (Jdg 1:16; Num 24:21). The deceit practised upon his royal host and the indiscriminate slaughter committed, lest any one should escape to tell the tale, exhibit an unfavorable view of this part of David's history.