In 1 Cor. 15:29 Paul says, “Otherwise, what will they do who are baptized for the dead, if the dead do not rise at all? Why then are they baptized for the dead?” (NKJV) It is said by commentators that there is broad disagreement as to what is being referred to by the phrase “baptized for the dead.” It is common to find in most commentaries an extended discussion of the verse with much more space being devoted to it than there is to the average verse.
I have no doubt that the verse is a reference to water baptism for the remission of sins (yes, I can hear my critics already). Why do I say that? In the very first chapter of First Corinthians Paul begins a discussion of the divisions in the church at Corinth. To show the brethren the error they were following in dividing up into followers of men he says, “Is Christ divided? Was Paul crucified for you? Or were you baptized in the name of Paul? I thank God that I baptized none of you except Crispus and Gaius, lest anyone should say that I had baptized in my own name.” (1 Cor. 1:13-15 NKJV)
This does not mean that only a few of those whom Paul converted in Corinth were baptized, not at all. Paul established the church in Corinth in Acts 18 and it is said there that “Crispus, the ruler of the synagogue, believed on the Lord with all his household. And many of the Corinthians, hearing, believed and were baptized.” (Act 18:8 NKJV) What were the Corinthians hearing?
They were hearing the entire gospel message (1 Cor. 15:3-4), “For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, and that He was buried, and that He rose again the third day according to the Scriptures.” (NKJV) They were hearing what was demanded of them to do—believe the message preached, repent, and be baptized for the remission of sins.
Remember who established the church at Corinth--Paul. He is the one doing the preaching. He is the one Ananias spoke to in Acts 22:16 saying, “Arise and be baptized, and wash away your sins, calling on the name of the Lord.” (NKJV) Is Paul who had to be baptized to wash away his sins, according to Ananias’ command, going to then turn around and tell the Corinthians, "Yes, I had to but you don’t?" Why are many of the Corinthians being baptized under Paul’s preaching? (Acts 18:8) To ask is to answer.
But, there is even more. In 1 Cor. 6:9-10 Paul gives a list of what were some real serious sins (they all are) and then says in the next verse, “And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God.” (1 Cor. 6:11 NKJV) Does the word “washed” here remind you of the word “wash” as in “wash away your sins” (Acts 22:16), the words of Ananias to Paul when he was yet known as Saul? So the church at Corinth, meaning each Christian in it, had been washed of their sins the same way Paul himself had in the waters of baptism (the place where the blood of Jesus is contacted spiritually).
Every Christian in Corinth, as were all in the first century, was baptized into Christ. “For as many of you as were baptized into Christ have put on Christ.” (Gal. 3:27 NKJV) That being the case, the truth, it necessarily follows that “as many of you as were not baptized into Christ have not put on Christ.” If one premise is true the other has to be as well.
But, we do not have to reason our way into getting the Corinthians baptized. Paul tells us specifically. “For by one Spirit we were all baptized into one body.” (1 Cor. 12:13 NKJV) He is writing to the Corinthians. He uses the word "all." This is not a passage about Holy Spirit baptism which only the apostles and the household of Cornelius received as far as we are told. It is the Spirit that taught the Corinthians the need to be baptized; it was the Holy Spirit within the inspired apostle teaching truth that would lead men and women to desire to be baptized and to do it.
What does all of this have to do with 1 Cor. 15:29 and the baptism for the dead--a lot. As Paul spoke to the Corinthians through his writing he was speaking to them of that which they knew--baptism for the remission of sins--and that which they had done.
1 Cor. 15:29 shows beyond any doubt that the Corinthians had been taught and firmly believed that baptism was essential to salvation or else why be baptized for the dead? We are always looking at this passage wondering who the dead were or what the meaning is but in doing so we overlook the obvious lesson. If baptism is a meaningless thing, only a symbol or sign, then why be bothered with it at Corinth or anywhere else and especially for the dead? If, on the other hand, it is essential for salvation the passage is easily understood as people desperate for the salvation of loved ones gone on who left this world in their sins.