Now that you've modified the obelisk with tech from the Sundial, there is only one more component needed: your Light. The obelisk is not yet active, but using your Light to charge it will allow you to bring it back to full power.
Charge the obelisk by defeating enemies with abilities and your Super, and by collecting Orbs of Light.
"The obelisks were created to keep my temporal experiments with the Sundial contained to Mercury. When I gave up my search for Saint-14, they fell into disrepair. I think your Light will be the spark to reignite their power." —Transmission from Osiris
Legendary Quest Step
2019.12.10 (Season of Dawn)