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.