Sylvester held some details back while openly revealing some others. The Guardians were the people he was going to leave the world to when he went to the Demon Realm, or focused on battling the two Primordial Gods, although he had no idea how he was going to do that.
"...These two Primordial Gods are more powerful than any entity you can imagine. Space, time, fate, past, present, or future; Everything rests within their control. They were the ones who forced Saint Scepter to do all that he did. They are the ones who destroyed all our knowledge that goes beyond five thousand years in the past. They killed all beings that knew about that era.