Albert Barnes Commentary 1 Samuel 14:18

"And Saul said unto Ahijah, Bring hither the ark of God. For the ark of God was [there] at that time with the children of Israel." — 1 Samuel 14:18 (ASV)

Instead of “the ark,” some scholars read “the ephod,” due to the improbability that the ark was with Saul at this time. This reading is also supported by the fact that the command “Bring hither” is never applied to the ark but is regularly used for the ephod (1 Samuel 23:9; 1 Samuel 30:7). Moreover, the ephod with the Urim and Thummim, not the ark, was the proper instrument for inquiring of the Lord.

If, however, the Hebrew text is correct, they must have brought the ark into Saul’s camp from Kirjath-jearim (1 Samuel 7:0), possibly to keep it safe from the Philistines.