Embora nem o filme nem o roteiro discutam especificamente quais poderes o amuleto possui ou concede, John dá a Angela como uma espécie de proteção. De o script :
John turns to her -- locks on those eyes. He reaches into his coat pocket as he walks up to her. She shudders as his arms wrap around her face and for a beat they're cheek to cheek. When he pulls back she sees he has clipped Hennessey's AMULET around her neck. JOHN Think of it as a bulletproof vest.
Aqui é onde o roteiro e o filme divergem.
No filme, Angela acidentalmente deixa o amuleto no carro quando ela tira o casaco e é quando John percebe o amuleto desaparecido que Angela é seqüestrada.
Então, adicionado ao comentário anterior de John para Hennessey, é razoável supor que ele oferece proteção contra ataques de demônios / mestiços.
Quanto ao motivo exato pelo qual ele tirou - ou, como no script, removeu o amuleto - vamos ver o script novamente.
HENNESSEY Oh God, you want me to surf the ether. He instinctively touches an AMULET around his neck. Four intersecting crosses. JOHN Come on, you know that exorcism wasn't right. HENNESSEY I... I don't have the Sight anymore. JOHN Don't have it or don't want to use it? Hennessey vacillates. This is obviously tough for him. JOHN Just look around. A few days. You spot anything unusual, anything -- you let me know. Okay? John wraps an arm around his shoulder like a good buddy, then reaches behind his neck -- JOHN It'll be like old times. -- and unclips the amulet from Hennessey's neck. That unnerves the big guy. John drops it in Hennessey's pocket. JOHN Just for a few days.
Isso reforça a ideia de que o amuleto é uma proteção. Ao removê-lo, John espera que os Demônios se aproximem de Hennessey e ele possa aprender algo.
Finalmente, temos a versão do roteiro da cena em que John e Angela encontram Hennessey na loja.
John leans down to the remains of his friend. A cop starts to intervene but Angela blocks him. Let him be. John has trouble taking this in, reluctantly reaches into Hennessey's coat pocket -- finds the protective amulet he himself removed from his friend. That's even more crushing.
Esta parte final praticamente confirma (pelo menos no IMO) que o amuleto deveria proteger o usuário de ataques demoníacos.