Spooky
Explanation
The Joke
The comic shows God and a biblically-accurate angel (depicted as a golden wheel covered in eyes, referencing the "ophanim" or "thrones" from the Book of Ezekiel) standing in Heaven. God says "this place is super spooky" and the angel stammers that it "g-g-gives me the c-c-c-creeps." The caption at the bottom reads: "Technically, Heaven is haunted."
The joke rests on a simple logical deduction: Heaven is full of the spirits of dead people. A place filled with the spirits of the dead is, by definition, haunted. Therefore, Heaven is haunted. It is an observation that is both theologically sound and absurdly funny -- reframing the eternal paradise of Christian theology as a giant haunted house.
The Humor
The humor works on multiple levels. First, there is the delightful absurdity of God himself being spooked by his own domain. Second, the angel's cartoonish fear (stuttering like a Scooby-Doo character) contrasts wonderfully with its bizarre, eldritch appearance -- the kind of being that would normally terrify humans. Third, the comic was published on November 1st (just after Halloween), making it a perfectly timed holiday joke. The deadpan caption sells the gag by presenting this ridiculous conclusion as a matter of dry technical fact.
References
The angel depicted as a wheel covered in eyes/triangular shapes is a reference to the biblical description of certain angels (ophanim/thrones) in Ezekiel 1:15-21 and Ezekiel 10:9-13, which are described as wheels within wheels covered in eyes. This style of "biblically accurate angel" became a popular internet meme.