I just realized a very interesting consequence of two theses that I'm sure many people hold. The first thesis is the Reformed version of infant baptism. I don't think the Catholic version has this result. Protestant paedobaptists believe that baptism does not save, nor remove original sin. It does indicate parents' trust that their child, being in the covenant community, will eventually develop personal faith and serve Christ as Lord. In other words, the content is pretty much what other parents express when they dedicate their children in hope of baptism when they express faith at an old enough age to be recognized as genuine. The biggest difference is that paedobaptists use the term 'baptism' and treat their children as part of the covenant itself rather than simply as benefiting from being part of the more general covenant community. As a credobaptist I disagree with this view, but it's quite common among the Reformed.
The second thesis is the main idea behind retroactive prayer. I've already argued for the possibility of legitimately retroactive prayer, so I won't do all that again. I'll simply say that if you accept that God has perfect knowledge of what's future to us (whether because he's outside time or some other reason), there's no reason for us not to pray about things that have already happened when we don't know the outcome. If God can foresee my prayer beforehand, then there's nothing to stop God from answering what I will later pray. The key idea here is foreknowledge, which all Reformed accept.
Now if you put these two things together, you get a very surprising result. The same things that justify these two views, when combined, will open up the possibility of baptism for the dead.
My argument is as follows. The key idea behind retroactive prayer is that God knows well ahead of time what we will pray. So it doesn't matter to God whether my prayer that my son will survive an open-heart surgery is before or after the operation itself. It matters to me. If I already know he didn't survive, it's foolish to pray that he would. I already know. But that's just parallel to what's the case if I already know that he won't survive, and I pray it ahead of time. If I already know that the world will be destroyed as if by fire because II Peter says so, and I pray to God that it won't happen, I'm praying something that I already know is in vain. It would be like a kid asking Mom to have bought a different color popsicle. It already happened, and you know the result. You can't change it.
It's different when we're considering God's providence. When God was working out how he would act at various times in history, he took into account what people would do, including how people would pray. This is true of prayers that are still future to us. So the point is that when we don't know the outcome, we can pray for something, and however it did turn out, even if it already happened, may have been because God took into account our prayer. So praying for something after it happens is not problematic, as long as you don't know the outcome of what you're praying for. It sounds weird, but it makes perfect sense when you spend a little time thinking about it. One of the elders in my congregation did exactly this sort of thing in our prayer times while another elder was ministering overseas. He would pray for him as he had preached earlier that morning. It seemed perfectly normal as he did it, because he knows God would have noticed this prayer when working out what would have happened earlier that day on the other side of the world.
When you combine this with the key idea behind paedobaptism, you get interesting results. Paedobaptists believe it's ok to baptize a child who doesn't know or approve of the baptism, who has shown no signs whatsoever of being elect to salvation. They believe this because they think baptism is a trust on the parents' part that their child will be saved, will express faith in Christ, and will serve him as Lord. They describe their attitude as expectant of their child's role in the covenant community as naturally leading to salvation.
Once you have these two things, I think there could be cases of baptism for the dead that would be perfectly appropriate. What if a family from a Baptist church decided they want to become Presbyterian? They become convinced that Presbyterians have it right, and they decide to express Presbyterian convictions by having their unbaptized children baptized. The only problem is that their oldest son, a teenager, was kidnapped three years ago. They discovered his body a month ago, and he had died hours before they found it. They have no idea what he'd been doing for the last few years. He hadn't expressed faith before he was kidnapped, but he hadn't given any sign that he had rejected God either. He simply hadn't made a clear choice. He wasn't old enough or mature enough for them to be sure. Should they trust that he turned out to have been elect? Should they trust that their raising him in the covenant community had the effect paedobaptists say they believe that it will have on all the kids they baptize as infants? I think the answer has to be yes. If they should now baptize all their other kids, it seems by the same reasoning that they should baptize their dead oldest son, in the trust that he is indeed elect and committed himself to Christ during that three-year time.
Now virtually no one but Mormons will accept this conclusion, though Mormons would never accept it on these grounds. I don't know their view on baptizing infants, but I know they deny divine foreknowledge. My challenge to people of Reformed persuasion is how they can deny my argument without abandoning their Reformed principles. I don't think it can be done without giving up what justifies retroactive prayer (divine foreknowledge) or what justifies paedobaptism (the possibility of baptizing someone against their own knowledge when you have no idea if the person is elect). When you put those things together, there will be cases of dead people whom it would be ok to baptize.