I replayed LOS1 recently and was struck with a thought. During the Oblivion Lake segment, Zobek mentions that the prophecy about the pure-hearted warrior claming the powers of the Lords of Shadow mentioned that this warrior would use the aquirred powers "in order to overcome all evil." It also said "this warrior would become God's vassel on earth... supremely powerful... he could do anything..."
I had originally thought that this was referring to the end of LOS1 when Gabriel overcomes Satan and frees the spirits back into heaven. But what if it is actually refering to the end of LOS2? In the prolouge, Dracula claims to be God's vassel or "Chosen One," and Marie tells Gabriel that his "suffering had to happen." What if God needed Gabriel to become Dracula in order for him to be powerful enough to kill Satan? It would explain why he favored Dracula in the prayer battle with Roland de Ronceval and blew the Brotherhood army to kingdom come. If the Brotherhood (or the Belmonts, for that matter) killed Gabriel then, no one would have the power to be able to destroy Satan forever.
This is just speculation on my part. I'd love to hear other people's thoughts on this.