Jamieson, Fausset and Brown on 1 Samuel 13:2

2. Saul chose him three thousand men of Israel--This band of picked men was a bodyguard, who were kept constantly on duty, while the rest of the people were dismissed till their services might be needed. It seems to have been his tactics to attack the Philistine garrisons in the country by different detachments, rather than by risking a general engagement; and his first operations were directed to rid his native territory of Benjamin of these enemies.

1Sa 13:3, 4. He Calls the Hebrews to Gilgal against the Philistines.