Paul’s reference to “those who are baptized for the dead” is one of the more obscure references in 1 Corinthians:
Now if there is no resurrection, what will those do who are baptized for the dead? If the dead are not raised at all, why are people baptized for them? (1 Corinthians 15:29)
Christian readers have made various strained attempts down the ages to provide palatable explanations such as “those children who are baptised following the example of their late Christian parents” – one of the lamer attempts to explain the verse, but the language used by Paul clearly points to some non-Christian, probably Jewish practice.
At this point it is worth remembering that the Greek verb baptizw (to wash the body) is not uniquely Christian, it is used both in the Greek Old Testament and New Testament for ceremonial washing, namely the masculine noun baptismos (ceremonial washing). It is only in the New Testament that this Greek verb baptizw also becomes associated with a new neuter concept noun baptisma (washing-ism, baptism) that is not found in any Jewish Greek or pagan Greek source and can only be assumed to be a Christian coinage to express washing literal and spiritual (John 3:5, Titus 3:5). So the suggestion here is that if 1 Corinthians 15:29 is referring to a Jewish practice, then it relates to baptismos-ablutions as practised by Jews, not full baptisma-baptism as practiced by Christians.
The only problem with that is that there is no washing “for the dead” in the Old Testament. And no teaching about prayer for the dead in the Old Testament. The Jews mourned for those who slept with their fathers in Sheol, but did not make intercessory prayer for them. Although prayers for the dead are a typical Egyptian and Ancient Near East practice documented in numerous Egyptian, Canaanite and Assyrian texts, there is not a single mention of such prayers in the Old Testament – typified by David’s attitude to the death of his and Bathsheba’s baby:
21 David’s servants asked him, “Why are you doing this? When the baby was alive, you cried and refused to eat. But when the baby died you got up and ate food.” 22 David said, “While the baby was still living, I cried and refused to eat because I thought, ‘Who knows? Maybe the Lord will feel sorry for me and let the baby live.’ 23 But now the baby is dead, so why should I refuse to eat? Can I bring the baby back to life? No. Some day I will go to him, but he cannot come back to me.” (2 Samuel 12:21-23)
The only examples of prayers for the dead among Jews are found outside the Bible, most famously in Judas Maccabeus’ prayers for those killed in battle:
Judas Maccabeus’ prayers for those killed in battle
38 Then Judas assembled his army and went to the city of Adullam. As the seventh day was coming on, they purified themselves according to the custom, and kept the sabbath there. 39 On the next day, as had now become necessary, Judas and his men went to take up the bodies of the fallen and to bring them back to lie with their kindred in the sepulchres of their ancestors. 40 Then under the tunic of each one of the dead they found sacred tokens of the idols of Jamnia, which the law forbids the Jews to wear. And it became clear to all that this was the reason these men had fallen. 41 So they all blessed the ways of the Lord, the righteous judge, who reveals the things that are hidden; 42 and they turned to supplication, praying that the sin that had been committed might be wholly blotted out. The noble Judas exhorted the people to keep themselves free from sin, for they had seen with their own eyes what had happened as the result of the sin of those who had fallen. 43 He also took up a collection, man by man, to the amount of two thousand drachmas of silver, and sent it to Jerusalem to provide for a sin offering. In doing this he acted very well and honorably, taking account of the resurrection. 44 For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead. 45 But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore he made atonement for the dead, so that they might be delivered from their sin. (2 Maccabees 12:38-45)
While it is unlikely that Paul has this particularly story in mind, it does give evidence of prayers for the dead, and the connection of that to resurrection in non-Biblical Jewish practice. Note that 2 Maccabees 12 does not actually mention the Numbers 19:11 rule of 7 days ceremonial uncleanness for soldiers burying dead comrades, but it is clear that ritual washing, .