The Lost Souls quest is a Codex challenge that you will be able to complete once you have made your way to the Shattered Temple in Throne and Liberty. The mission looks pretty easy on the surface and you will be tasked with putting some souls to rest for a Purelight Wizard.
However, completing the Lost Souls quest is easier said than done, and there are many in the community who are having a hard time completing it.
Here is a guide that goes over how you will be able to easily complete this Codex challenge in the MMO.
How to complete the “Lost Souls” Codex challenge in Throne and Liberty

To complete the Lost Souls mission here are a few steps that you will need to do:
1) Talk to the Wizard at Light Sanctum Ruins
Make your way to the Light Sanctum Ruins in the Shattered Temple region to find the wizard. You will find the NPC standing infront of a pit that is filled with the undead. So interact with them and then touch the ghost orb which is at the very bottom of the pit.
2) Interact with the Soul Magic Orb
The next thing you will need to do is to go to the inner portion of the ruined tower by teleporting to the waypoint. You will need to climb the tree branches and then jump in through the open window.
You will find the Soul Magic Orb then. Interact with it to touch it, and this will then cover your body in blue flames.

3) Extinguish the flames
Once you are character is on fire, you will need to extinguish the flames by using the Glide Morph and then reaching the waterfall which is close by. To reach it, you will need to head out of the window close to the Soul Magic Orb and then jump out of it. Use the Glide Morph to reach the waterfall on the right.
Just touching the water will extinguish the flames.
4) Head back to the Wizard
Now make your way back to the quest giver, who will then thank you for all the work that you have done. This will round out the quest and you will get some Precious Armor Growthstones and Precious Polished Crystals for your efforts.