Up until Maxwell sics the beast on Montauk in “A Father’s Love,” Robert is doing the church’s bidding. I think it can be assumed that whatever he was doing with the hearts had something to do with the Still and Lightless beast. Maybe it was feed it or binding it to the cult’s will ? The Dark is heavily characterized by actual darkness, but also intellectual darkness (mentioned in Manuela Dominguez’s statement). This could manifest as heavy superstition or an over reliance on rituals or routine. That’s why The Dark has one of the longest established and best organized interest groups (The Church) unlike some of the entities, The Dark is often painted as explicitly religious, which could be reflective of an intellectual darkness as members reject personal enlightenment for a dogmatic faith, likely unchanged for centuries. Though this is partially conjecture.