Okay, this is legitimately weird. Barabas has been killing people left and right, way caught up in the hustle and flow of his schemes, and within the space of a few breaths he goes from being the master puppeteer to…burning to death in a caldron? There are presumably a lot of ways to do away with your Machiavellian villain (we are, after all, talking about a guy who murders people with bouquets of flowers), so why did Marlowe choose this one?
Try to visualize it: Barabas is up on stage, and at the critical moment Ferneze cuts the rope and Barabas basically falls into a fiery pit. When you look at it that way, the caldron looks like a pretty clear representation of the Christian hell. At first glance, that makes sense: the Christian leader is sending the villainous infidel down to hell. And, for the record, Judaism has no concept of hell, so if you read it as face value this scene can look like Ferneze getting to deliver the ultimate religious I Told You So.
Two things that make this tidy reading a problem:
(1) Hell doesn't correct Barabas. If he were really going to Hell, you'd expect some sort of moment where he sees the light, repents, and dies regretting his wrongs. He doesn't, though, because (a) that's just not his style—Barabas dies scrappy and mad, not meek and remorseful—and (b) that kind of ending could make you think that this play is an affirmation of Christianity which it…really isn't.
(2) It might seem like Barabas going to Hell is a ringing endorsement of Christianity. Well, Barabas's relationship with the canon of Jewish beliefs is…complicated, to say the least.Soon after having everything taken away from him, Barabas curses his enemies, saying, "I ban their souls to everlasting pains, / And extreme tortures of the fiery deep, / That thus have dealt with me in my distress!" (1.2.165-67).
Sounds just like hell, right? By talking about the"extreme tortures of the fiery deep," Barabas makes the cauldron sounds not much like the run-of-the-mill Christian hell as the same horrifying torment that Barabas wanted to send his own enemies to. In short, it's not the hell of the Christian god, but the punishment that Ferneze and Barabas have mutually devised for each other through their hatred.