Unlike errands, side quests typically reward more than just XP, and if you complete this side quest you will gain a permanent increase to your spear damage. In order to craft the Fire Arrows ...

His attacks include a ranged homing fireball, a standard thrust with his spear ... While you need to find Fire Knight Queelign one more time to finish the quest, you don’t need to fight him ...

Completing Ironeye's Remembrance quest in Elden Ring Nightreign is required to obtain a unique Relic that provides useful buffs.