Albert Barnes Commentary 1 Samuel 13:15

"And Samuel arose, and gat him up from Gilgal unto Gibeah of Benjamin. And Saul numbered the people that were present with him, about six hundred men." — 1 Samuel 13:15 (ASV)

Samuel arose - Saul could not return to his own station at Michmash, since it was occupied by the Philistines; so, perhaps by Samuel’s advice (as the text indicates he preceded him there), he joined Jonathan at Gibeah. Some would read “Saul” instead of “Samuel.”