One rule in poetry, prose poetry, even genre-bending poetry-prose combos like The Marriage of Heaven and Hell is this: don't confuse the writer with the speaker. You see, Shmoopers, writers are sneaky creatures. Even though they might be using a first-person point of view, they could be hiding behind an invented character and speaking as them, rather than of themselves.
Blake seems to be doing that here. After all, do we really think that Blake himself had a meal with biblical prophets, visited Hell's publishing house, and convinced an angel to turn himself into a devil? That's just crazy. Surely Blake is using his speaker like a kind of imagined, devilish anti-hero. Right?
Well, let's look a bit closer. We learn in the first section of the book that it's been 33 years since the rise of a "new heaven," one that the speaker also refers to as "the Eternal Hell" (1.23). (Remember that our speaker is actually a fan of Hell—at least as it's defined by conventional religion—because that's where the people who indulge their impulses wind up.) That number 33 seems pretty significant to us. For one, it's the age of Jesus when he was crucified. And, it also happens to be the age of… William Blake when he wrote this. Coincidence? Let's read on.
In the first "A Memorable Fancy" section, the speaker tells us about something he saw on "a flat-sided steep [that] frowns over the present world" (3.2). Specifically, he "saw a mighty Devil folded in black clouds […] with corroding fires he wrote." Hmm—this sounds an awful lot like Blake himself, looking down on the world and using a corrosive method (like copper engraving) to write. Later, our speaker makes a pledge to use this same technique: "the notion that man has a body distinct from his soul is to be expunged; this I shall do by printing in the infernal method by corrosives" (5.13).
Still later, the speaker has an argument with an angel, in which he convinces that angel that Jesus actually broke each of the Ten Commandments. Even still, "Jesus was all virtue, and acted from impulse, not from rules" (8.3). The speaker is so convincing that the angel converts into a devil on the spot. This is another section of the book that makes us say "Hmm," because here our speaker is putting forth an argument in favor of impulse and against conventional religion—both of which are ideas that were near and dear to Blake's heart.
So, to sum up: we have a speaker who may be the same age as Blake, who uses the same printing techniques as Blake, and who feels the same way as Blake. So maybe our speaker is just a thinly disguised version of… Emmanuel Swedenb—nah, it's Blake. We know that we said it's dangerous to mix up speakers and writers, but here the similarities are just too many to ignore. Whether he's directly drawing parallels to Blake's biography, or observing other people (or devils) that are doing some classically Blake-ian things, it's a safe bet to read the "I"s and "me"s in this poem as coming directly from Blake himself.
Of course, that doesn't mean that he really and truly traveled to Hell. Given that the speaker is pushing Blake's ideas forward at every turn, a better way to read his adventures in the underworld is as satire. In particular, Blake is poking fun of Emmanuel Swedenborg's Heaven and Hell, which saw that author taking trips through the afterlife, but not really telling us anything new about it. Blake, unhappy with that portrayal, uses the same set-up and positions himself as the star of the show, happily pointing out how Swedenborg got, well, pretty much everything all wrong.