Destiny 2 features the Legendary Quest Spirit of the 14th Saint. This quest has a total of nine steps that you need to complete to complete the quest.
One of these steps requires that you find the spirit of the 14th saint:
An impossible task – Saint-14’s Ghost
The Vex transponders you planted have detected a network signal at the Pools of Luminance at the Cistern. Head there and see if you can open a gateway to the Vex network on Nessus.
Saint-14's Ghost Location
To find the Saint-14's Ghost you have to travel to the planet Nessus. Land there at the cistern and then go to the gate location.
The path can be a little confusing and difficult to explain, so we've included a video below.