How do i get the seeker of light set?
Kill mobs - they might drop it
Gamble bloodshards at Kadala
Use the Cube’s upgrade rare to legendary recipe
Group up with another Crusader and ask them if they’ll drop any of that set for you
You get the seeker of light set just as any other piece of gear, by farming loot.
Preferably as a Crusader, since that makes dropping crusader gear much more likely.