Priest Cerenas:
If you enter the Imperial Tomb, or fight in the Shrine of Loyalty near the Wall of Argos, you will be able to meet the Archon or Inferiors of Halisha. You can get this amulet if you defeat them.
Do you understand? If you want this amulet, you need to defeat Halisha's Inferiors or Archon. The Resonance Amulet will let you know where the fifth tablet is.