Charles Ellicott Commentary 1 Samuel 30:1

"And it came to pass, when David and his men were come to Ziklag on the third day, that the Amalekites had made a raid upon the South, and upon Ziklag, and had smitten Ziklag, and burned it with fire," — 1 Samuel 30:1 (ASV)

On the third day: That is, on the third day after King Achish, due to the objections of the Philistine chieftains, had dismissed David and his contingent from the ranks of the Philistine army. This dismissal likely did not take place at Shunem, in the Esdraelon (Jezreel) Valley, because Shunem is some ninety miles distant from Ziklag. Achish's division had marched from Gath with David, and the event where David’s services were dispensed with occurred somewhere in Philistia, after the entire force had assembled.

The Amalekites had invaded the south. This was partly in retaliation for David's recent raids in the Amalekite country, and partly because Amalek had heard that, since the Philistine and Israelite armies had left the southern districts for the central part of Canaan, the entire south country was left unguarded. "The south," that is, "the Negeb," or the dry land—all the southern part of Judea; it also included a part of the Arabian Desert.

And smitten Ziklag. This was an act of vengeance, as Ziklag was the city of that famous Israelite chieftain David, who had done so much damage to Amalek, and who had treated the captives with such cruelty. While other parts of the south were merely plundered, Ziklag was marked for utter destruction: it was sacked and burned.