Second Coming
Explanation
The Joke
A person prays to Jesus, asking when he will return to Earth. Jesus replies that he will come back "when it is on Earth as it is in Heaven." When asked when that will be, Jesus answers "about 30 years." The person is surprised and asks why then. Jesus's answer: "I like the thermostat wayyyy up."
The Humor
The joke works on multiple levels. First, it references the Christian theological concept of the Second Coming, in which Jesus is prophesied to return when Earth mirrors the kingdom of Heaven. The twist is that Jesus interprets "on Earth as it is in Heaven" not in a spiritual or moral sense, but in a purely physical one — he wants the temperature to be really high, like a stereotypical old person who cranks up the thermostat.
The "about 30 years" timeline is a dark reference to climate change. The implication is that in roughly 30 years, global warming will have raised Earth's temperature enough to match Jesus's preferred thermostat setting. So the Second Coming isn't triggered by humanity achieving moral perfection — it's triggered by catastrophic global warming making the planet toasty enough for Jesus's personal comfort.
Broader Context
This is part of Weinersmith's "Second Coming" series of comics, which repeatedly imagines Jesus's return with various irreverent twists. SMBC frequently uses theological setups to deliver jokes about science, climate, or human nature.