Istel is a key NPC who is a core part of the Mother’s Gift mechanic in Diablo 4 which was introduced to the RPG in Season 5, Season of the Infernal Hordes. As you make your way through the challenges in the new Seasonal Journey you will eventually start The Wages of Hatered questine.
However, to be able to complete the mission and continue with the story of the Mother’s Gifts, you will need to find Istel in Zarbinzet. The NPC is not that easy to locate, and many in the community are quite confused as to how to find her.
How to find Istel in Zarbinzet in Diablo 4 Season of the Infernal Hordes

To find Iztel you will need to head to the eastern gate in Zarbinzet and you will find the NPC next to a soldier. The quest to locate her will activate after she leaves her family house and you will see a large green circle around the entire town.
So to find her, just make your way to the eastern gate in Zarbinzet, and you will find Istel standing next to a soldier and the bodies of enemies who are pinned to crosses.
These enemies are the same ones that attacked you and Istel in her family’s house. So once you approach her, the green circle around town will disappear and you will get the green leaf seasonal icon over her.
So just walk up to her and interact with her to start the next part of the quest line. As you progress through the mission, you will eventually reach the final stages of The Wages of Hatred.
To round it out, you will just need to make your way back to the room where you claim rewards with Mother’s Gifts and search for the Grimoire that is placed on the table. Interact with it, read it, and end this part of the seasonal journey in Diablo 4.
After you round out the quest you can go back to farming Mother’s Gift and Unique items like the Shard of Verathiel by completing the new Infernal Hordes and Hellbreach Dungeons.