John Gill Commentary 1 Samuel 13:4

"And all Israel heard say that Saul had smitten the garrison of the Philistines, and also that Israel was had in abomination with the Philistines. And the people were gathered together after Saul to Gilgal." — 1 Samuel 13:4 (ASV)

And all Israel heard say that Saul had smitten a garrison of
the Philistines
For though it was smitten by Jonathan, yet it was by the order of Saul, and so ascribed to him; it seems to be a concerted thing to fall upon the garrisons of the Philistines, and get them out of their hands, and so deliver Israel entirely from them; but it was not wise for Saul, if he had such a scheme in his head, to disband his large army, as he had lately done:

and that Israel also was had in abomination with the Philistines ;
who were highly incensed against them by this action, and vowed revenge; the name of an Israelite was abhorred by them; and perhaps this action might be attended with much craft and cruelty; and if these garrisons were held by agreement, they might charge them with perfidy, with breach of articles, and so their name was made to stink among them, as the word signifies:

and the people were called together after Saul to Gilgal ;
by sound of trumpet.