Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
David, with characteristic Oriental subtlety (compare Sa1 21:2), suggests as a reason for leaving Gath that his presence was burdensome and expensive to the king. His real motive was to be more out of the way of observation and control, so as to act the part of an enemy of Saul, without really lifting up his hand against him and his own countrymen of Israel.
Ziklag - This was properly one of the cities of Simeon within the tribe of Judah (marginal references), but it had been taken possession of by the Philistines. The exact situation of it is uncertain.
Unto this day - This phrase, coupled with the title the kings of Judah, implies that this was written after the revolt of Jeroboam, and before the Babylonian captivity.
The Geshurites bordered upon the Philistines, and lived in the mountainous district which terminates the desert on the northeast (marginal reference). They were a different tribe, or, at least, a different branch of it, from the Geshurites who lived on the northeast border of Bashan, and were Arameans Sa2 15:8. The Gezrites, or Gerzites, may be connected with those who gave their name to Mount Gerizim.
The Jerahmeelites - i. e. the descendants of Jerahmeel, the son of Hezron, the son of Perez, the son of Judah (marginal references). They were therefore a portion of the "south of Judah."
The Kenites - See Num 24:21 note; Num 4:11; and for their near neighborhood to Amalek, see Sa1 15:6.
Tidings - The word is not in the original. The sense rather is "to bring them to Gath," as captives and slaves. The prisoners taken would naturally have been part of the spoil, but David dared not to bring them to Gath lest his deceit should be discovered. Obviously these tribes were allies of the Philistines.