He could just use water from a well nearby, right?

Yeah, I don’t get this.

In John, there’s a wedding and the planners forgot to bring the booze, so Jesus tells some dudes to fill a bunch of casks with water, and then poof kablamo, they are made into wine via the power of Jesus being irritated.

There’s certainly a lot of imagery and focus on the blood of Jesus in the Bible… but the whole transsubstantiation/consubstantiation thing is about … the reverse of this, wine either transforming into, or metaphorically representing the blood of Christ.

I am… not aware of any part of the Bible nor sect/branch/denomination/church that teaches that Jesus at any point turns his blood into wine.

I don’t think that even happens in any of the ‘expanded universe’ / Gnostic texts.

In summary:

Wine -> Blood? Yes*.

Water -> Wine? Yes.

Blood -> Wine? No.

Some Christians (at least roman-catholic) celebrate communion, consuming ‘bread’ and wine that has been blessed. According to them the bread and wine literally become body and blood of Christ. That’s the joke of the comic :)

Yes but that’s backwards of what the comic is representing.

As I said… I don’t think any kind of Christian believes that Jesus’ blood ever turns into wine.

That doesn’t happen anywhere in the text.

So… the joke is… based off of a thing that doesn’t happen?

It would be like making a joke based off the idea that Moses can summon floods.

He can’t. He’s never shown to be able to do that, he’s shown to be a water bender who can move water out of the way, but not generate it.

doesn’t happen anywhere in the text.

Religion is more than just the book. Catholics literally believe that the wine at mass is literally Jesus’ blood. This is a joke about them. Not about the book that their specific flavor of whatever is based on.