Bringing people back from the dead is probably not a very good thing to do. If Gabriel tries to bring hos dead wife back, something bad is gonna happen. Maybe he will sell his soul to the devil/dracula/whoever by doing so.
Hence the line "I am your God now, Gabriel".
The two masks are obviously interconnected, so using one of them will most likely affect the other. Like, bringing a person back from the dead will kill another person. Or maybe; Bringing a pure hearted person back to life (Marie) will also bring a BAD person back to life (Dracula).
Lol, the plot will probably be something completely different though.
Or something.