Alright, here goes.
Let’s assume for a moment that the briefcase does contain Marsellus’ soul. The combination for the briefcase is: 666. Perhaps the Devil took Marsellus’ soul (possibly from the back of his neck, hence the band-aid that Jermo mentioned) and placed it into a briefcase. Tony gets a hold of it and passes it along. Marsellus finds out that Tony has something of value to him (an understatement) and tosses him out of a window. The fact that Tony can’t speak properly anymore is the Devil’s way of literally keeping his mouth shut.
And speaking of souls and how beautiful they are, it is likely that Marsellus’ soul is not that beautiful. But maybe his soul actually is beautiful, meaning that he is actually a good guy, and he just needs it back, so that he won’t be an a$$hole anymore. When Butch goes to the apartment to get his watch, he shoots and kills Vincent. After leaving, he runs into Marsellus (with his car) and they end up fighting. But, after Butch saves his life, Marsellus agrees to let him go, and they call it even. I think that this is influenced by the fact that Marsellus’s soul had been restored. Otherwise, he might not have been so lenient.
Now, back to the “Divine Intervention” scene. Jules and Vincent expected to have been blown away, But they were spared by “some strange coincidence”. Again, I think this is God allowing them no harm until they have completed their task. After the task is completed, they are no longer protected by his will. (This is why Vincent had no chance when Butch gunned him down.)
Now on to the date between Vincent and Mia Wallace. They go out, dance, have a great time, she re-establishes my point that no-one really knows why Tony was thrown out of the window, and later she ends up putting a little too much heroin up her nose. In my opinion, Vincent is in no way to blame for her near-death, but I don’t think Marsellus would agree. As Vincent puts it to his dealer, “If Marsellus finds out about this, I am a f***in’ grease-spot!” So they end up saving her life, and Vincent gets off the hook. What would happen if she had died of her overdose? Marsellus would probably have had Vincent killed, so then Vincent wouldn’t have been able to help deliver the case, and also wouldn’t have been available to help Jules out in the diner when he was talking with “Ringo”. And on that note, Pumpkin and Honey-Bunny also learned a valuable lesson when they found out what exactly they were dealing with, and what Jules’ cargo was. But before all of that, Jules and Vincent were still just talking, and Jules mentioned that he was thinking about the miracle they witnessed. But carrying something sacred like that is, to me, what convinced Jules that he was living the wrong lifestyle. And even earlier, when “The Wolf” tells them to move out of the sticks and get a cab, they decide to go and have breakfast. Once again, this breakfast proved fateful, and Jules learns about what he feels is his destiny. Not only that, but he sets himself on the path that he now feels is right, and making himself broke by giving all the money he had to the couple, strengthening the love they had for each other, and all the while saving everyone else from being robbed or killed.
I’m sure there may be some details I forgot, but if anyone has any to add, or any criticism to offer, please do. 😉