@Bilbool & Liiv
You need to place the painting on the altar. The painting can be found inside the room before you go to the altar (2nd room), painting that said "Responsible" if I'm not wrong remember it. After place that painting on the altar, secret door will open and you'll find Arhu. You need to use your vision and vampiric to steal source from spirits that binding him, then prepare for battle against Kemm.
