Baptism for the Dead?

 "Otherwise, what do people mean by being baptized on behalf of the dead? If the dead are not raised at all, why are people baptized on their behalf?" 1 Corinthians 15:29

The context here was the resurrection of Christians from the dead. Baptism for the dead was mentioned AFTER a teaching on the order of God's eschatological schema. The issue being addressed is the resurrection of the dead in general as a concept. Paul previously described Jesus as a new Adam, the progenitor of a new humanity with "translated" divine bodies. He taught that Jesus is not meant to simply be a part of our mortal life, ending in permanent death. Paul's Jesus will one day resurrect the dead Christians and also change the bodies of the living Christians into pneumatic (mistranslated as "spiritual") bodies like his own.

πνευματικός: pneumatikos. Mistranslated to "Spiritual" in most English Bibles.

In the Greco-Roman cultures, the concept of the pneuma ("spirit") was often associated with life force or breath, a notion that carried over into early Christian thought. This concept dovetailed smoothly with a common Jewish interpretation of Genesis 2:7 "Then the LORD God formed the human (adam) of dust from the ground and breathed into his nostrils the breath of life, and the man became a living nephesh (creature, soul). Genesis 2:7. God made the person out of dust and magically animated him with some of his divine life essence by breathing into his nostrils. The god's breath contained his life-giving power. This magically kickstarted the person's breathing, bringing life to the dust man. Now he is called a nephesh, translated as living creature or soul in the KJV. The Hebrew word for soil is adama, אֲדָמָה. The word for human is adam, אָדָ֣ם. The word for blood is dam, דָם. You can look at the similarities in the words and surmise something like a human is soil with living blood in it: adam/human, soil/adama, blood/dam. The idea that life is in the blood is mentioned in Leviticus 17:11. "For the soul/(nephesh) of the flesh is in the blood/dam." 

The oldest copies of Genesis and Leviticus date back to the second century BCE in the Dead Sea Scrolls (DSS). Most modern scholars Genesis was redacted into its final form around 400 BCE. Leviticus is believed to have been finalized between 600 and 300 BCE. Leviticus 17:11 reflects the Babylonian ancient near eastern concept of human life connected with blood when the first humans were created. In the Babylonian myth, Enuma Elish, the god Ea created the first humans from the blood of the slain god, Kingu, to do the work of the gods so the gods may be "set free" of their labors. Another Babylonian myth describes the first humans being made from clay for the purpose of doing the hard work so the gods could be relieved of it. In these we see the motif that humans were created and enlivened by gods, from clay (soil), and blood, to do work for the gods. This motif is echoed in the second Genesis creation myth, of Adam and Eve, in Gen 2:4-24.  

When Alexander the Great conquered the Levant in the early second century BCE, the Hellenistic culture took dominance over the conquered lands, including Judea. They had somewhat similar thinking as the ancient near eastern peoples, with more developed ideas recorded by Greek philosophers. This was when their complex theory of the soul/psyche was thoroughly developed and became of predominant importance. They taught that the pneuma (spirit, breath) is connected with the psyche (soul), which animated the body. The psyche/soul lived on after death, exiting the body as a small breath or puff.  

The early Christians, influenced by Jewish and Hellenistic ideas which permeated the thinking of the culture, understood the pneumatic realm as the domain of God and His activities, much the same as pagans believed about all their gods. The pneumatic (breath, vapor, airy) realm was a superior part of the world also called heaven or the (upper) heavens. The gods had pneumatic bodies. Yahweh and the resurrected/translated Jesus had the same pneumatic bodies. These bodies were commonly understood to be immortal, above sickness, had magical powers to defy what we now know to be the laws of physics, etc.

Paul was arguing that our hope in Messiah is NOT just for this life 1 Cor 15:19. Believers should be putting their hope in being resurrected/translated into immortal pneumatic bodies when the parousia (messiah's return) happens.

Apparently, some Corinthians weren't accepting that Jesus will resurrect their dead. Paul was trying to convince them otherwise. He then moved on to describe their future pneumatic bodies and the transformation they'll undergo into those bodies. He argued that he risked his life for Jesus BECAUSE he believed in a resurrection of the dead. And he supplemented his argument appealing to those who are baptized on behalf of the dead. That practice he described in the context of Christians having hope in a future resurrection. Pagans aren't in mind. Christians are.

If Paul was at all consistent in his letters, we can draw from his letter to the Thessalonian church for clarification of exactly who does or doesn't believe in a bodily resurrection. He emphasized that these were Christians specifically who baptized for the dead when he contrasted them with pagans who had no hope for a resurrection.

1 Thessalonians 4:13-14
But we do not want you to be uninformed, brothers, about those who are asleep, that you may not grieve as OTHERS DO, WHO HAVE NO HOPE. For since WE BELIEVE THAT JESUS DIED AND ROSE again, even so, through Jesus, God will bring with him those who have fallen asleep."

Paul contrasts "we", Christians who profess Jesus died and resurrected, with "others" who have no hope of being resurrected.

So, Paul was referencing certain Christians who were baptizing on behalf of the dead. This apparently was something Paul thought was an acceptable Christian ritual. What was the ritual? He didn't say. The only thing we have written about it is from the second century and later. So, the surviving descriptions of the baptism for the dead are not necessarily the same ritual Paul referred to. But these descriptions are particularly of interest when considering the mysterious baptism for the dead Paul mentioned.

The Marcionites baptized for the dead. John Chrysostom (late 4th century) described a baptism ritual of the Marcionites. "For if one of their catechumens dies, they conceal a living person beneath the bier of the departed, approach the corpse, talk with the dead person, and ask him whether he intended to receive baptism. Thereupon the person who is concealed, speaking from beneath for the other who does not answer, avers that he did indeed plan to be baptized, and then they baptize him for the departed one."

The Cerinthians were a sect of Christians around the late 1st/early second century who followed the teachings of Cerinthus. He taught divergent unique doctrines about Jesus which were soon rejected at large after his death. They're reported to have had a baptism for the dead. It's possible that their baptism for the dead did trace back to whatever Paul mentioned about it, being that they were around not too long after his death. Epiphanius of Salamis (4th century) explained their baptism for the dead ritual: "When some of them die before being baptized, others are baptized in place of them, in their name, so that when they rise in the resurrection, they may not have to pay the penalty of not having received baptism and become subject to the authority of the one who made the world."

Being that those accounts were written so long after Paul's time, it's hard to say whether they are completely accurate records having been written and passed down through so many generations. Although it's not impossible that they could be.

The Marcionites, on the other hand, came after Paul was long since dead. They were devoted to Paul's teachings very specifically. It's possible that their baptism for the dead stemmed from whatever Paul referred to. But their rejection of the Hebrew Bible and its God doesn't agree at all with Paul's writings. So, their rituals may likewise not necessarily trace back to Paul. Their baptism for the dead might be based off an interpretation of 1 Corinthians.

That's as close to an explanation we can have based on the evidence. Either way Paul described a baptism done by living Christians on behalf of dead people. And it's really not far off from modern Christian baptism. Modern baptism involves the Christian identifying personally with the death and resurrection of Jesus. Jesus died. They're identifying with his death in baptism as though symbolically accepting his death as atoning for their sins personally. So being baptized in proxy of someone who had died without having been baptized isn't a far stretch when considering the variety of methods and explanations given in the New Testament, early church writings, and archaeology as to how and why to baptize in the first century.

In conclusion, modern baptism is grounded in both Jesus's command to baptize converts and a variety of church traditions. The New Testament never describes how or why baptism was done. The authors assume the readers already know what baptism is, leaving future generations of readers in the dark about it. We know there were a variety of baptism methods and rituals. But we have no evidence of when, where, how, or why the first Christians were baptized. We only know it involved water, and it was traditionally ascribed to being first commanded by Jesus. One would think if the Son of God commanded all believing people everywhere to be baptized, we'd have something written explaining the details. But we are left today being forced to speculate.