As much as he was anti-Swedenborg, Blake was pro-prophet. He considered himself a prophet, after all, so it's not at all surprising to find multiple prophets in The Marriage of Heaven and Hell. In fact, this book reads a bit like Where's Waldo?, if Waldo were a biblical prophet instead of some weird dude in a red striped shirt. Lucky for you, we're here to point these guys (yes, they're all guys) out.
This may come as a shock to you, but Blake had a pretty active imagination. He went so far as to develop his very own set of mythological-philosophical characters, and among those is Rintrah. Rintrah is characterized by a bunch of shouting, fist pounding, and dirt kicking. In other words: dude is mad.
Blake saw him as a symbol of wrath, but not just in the way we think of being angry or seeking vengeance. Instead, this was due to the frustration at being confronted with injustice or wrongheadedness. In this way, Rintrah was a prophet who foretold a better way, or at least warned the world when it was on the wrong track. Think of him as your driver's ed instructor, one who "roars and shakes his fires in the burden'd air" (1.1)—or, you know, shouts right in your ear when you make a wrong turn.
In first section of The Marriage of Heaven and Hell, Blake gives his reader's homework: go read the Bible, specifically Isaiah, Chapters 34 and 35. In those chapters, the prophet Isaiah is saying two things to the people of Israel: 1) change your ways or terrible destruction is coming and 2) happy days are on their way. Isaiah is known for this good-cop, bad-cop routine, but his goal is to bring about change by foretelling the consequences of wrongheadedness. Sound familiar?
Blake even brings Isaiah, along with Ezekiel, into his writing in the book's first "Memorable Fancy" section. He asks them how they knew that God was actually speaking to them, to which Isaiah replies "I saw no God, no heard any […] but my senses discovered the infinite in everything" (5.2). In this way, Isaiah sounds a lot more like a poet than a traditional prophet, which is one of the points Blake is trying to make in this book: all our original ideas of God come from poets, not priests.
Much like Isaiah, Ezekiel is a biblical prophet who foretold of awful destruction and harmonious salvation. Much like Blake, he did so with a heaping dose of weird and troubling imagery. His role in The Marriage of Heaven and Hell is to discuss the role of "Poetic Genius" in the founding of religious thought. More specifically, he says: "We of Israel taught that the Poetic Genius […] was the first principle, and all the others merely derivative" (5.5).
In other words, Ezekiel—like Isaiah—reps the role of poetry as the founding force of religion. He also explains why he "ate dung, and lay so long on his right and left side" (5.9), which pretty much sounds like the worst time ever. For Ezekiel, though, it was totes worth it, since it helped him to satisfy "The desire of raising other men into a perception of the infinite" (5.9). We're… going to take your word on that one, Ezie.