Albert Barnes Commentary 2 Kings 13:17

"And he said, Open the window eastward; and he opened it. Then Elisha said, Shoot; and he shot. And he said, Jehovah`s arrow of victory, even the arrow of victory over Syria; for thou shalt smite the Syrians in Aphek, till thou have consumed them." — 2 Kings 13:17 (ASV)

Eastward - The Syrian kingdom of Damascus lay partly east, but primarily north, of the Holy Land. The arrow was to be shot eastward, not so much against Syria proper as against the location of their recent successes in Gilead (2 Kings 10:33), which was also to be the site of Joash’s victories over them. Aphek is almost due east of Shunem, where it is likely that Elisha was at that time.

The arrow ... - This is literally, An arrow of deliverance from the Lord, and an arrow of deliverance against Syria; and you will strike the Syrians in Aphek until they are destroyed.