Has to do with false teachers. Note that Paul says "Why are they"??? Not why are we in the church.
Barnes commentary is also along the lines of Clement>>>>>1 Corinthians 15:29>>but states the reality of facts is lost and goes on to state some possible practices.
Barnes' Notes on the Bible
Else what shall they do ... - The apostle here resumes the argument for the resurrection which was interrupted at
1 Corinthians 15:19. He goes on to state further consequences which must follow from the denial of this doctrine, and thence infers that the doctrine must be true. There is, perhaps, no passage of the New Testament in respect to which there has been a greater variety of interpretation than this; and the views of expositors now by no means harmonize in regard to its meaning. It is possible that Paul may here refer to some practice or custom which existed in his time respecting baptism, the knowledge of which is now lost. The various opinions which have been entertained in regard to this passage, together with an examination of them, may be seen in Pool's Synopsis, Rosenmuller, and Bloomfield. It may be not useless just to refer to some of them, that the perplexity of commentators may be seen:
(1) It has been held by some that by "the dead" here is meant the Messiah who was put to death, the plural being used for the singular, meaning "the dead one."
(2) by others, that the word "baptized" here is taken in the sense of washing, cleansing, purifying, as in
Matthew 8:4;
Hebrews 9:10; and that the sense is, that the dead were carefully washed and purified when buried, with the hope of the resurrection, and, as it were, preparatory to that.
(3) by others, that to be "baptized for the dead" means to be baptized as dead, being baptized into Christ, and buried with him in baptism, and that by their immersion they were regarded as dead.
(4) by others, that the apostle refers to a custom of vicarious baptism, or being baptized for those who were dead, referring to the practice of having some person baptized in the place of one who had died without baptism. This was the opinion of Grotius, Michaelis, Tertullian, and Ambrose. Such was the estimate which was formed, it is supposed, of the importance of baptism, that when one had died without being baptized, some other person was baptized over his dead body in his place. That this custom prevailed in the church after the time of Paul, has been abundantly proved by Grotius, and is generally admitted. But the objections to this interpretation are obvious:
(a) There is no evidence that such a custom prevailed in the time of Paul.
(b) It cannot be believed that Paul would give countenance to a custom so senseless and so contrary to the Scripture, or that he would make it the foundation of a solemn argument.
(c) It does not accord with the strain and purpose of his argument. If this custom had been referred to, his design would have led him to say, "What will become of them for whom others have been baptized? Are we to believe that they have perished?"
(d) It is far more probable that the custom referred to in this opinion arose from an erroneous interpretation of this passage of Scripture, than that it existed in the time of Paul.
(5) there remain two other opinions, both of which are plausible, and one of which is probably the true one. One is, that the word baptized is used here as it is in
Matthew 20:22-23;
Mark 10:39;
Luke 12:50, in the sense of being overwhelmed with calamities, trials, and sufferings; and as meaning that the apostles and others were subjected to great trials on account of the dead, that is, in the hope of the resurrection; or with the expectation that the dead would rise. This is the opinion of Lightfoot, Rosenmuller, Pearce, Homberg, Krause, and of Prof. Robinson (see the Lexicon article Βαπτίζω Baptizō), and has much that is plausible. That the word is thus used to denote a deep sinking into calamities, there can be no doubt. And that the apostles and early Christians subjected themselves, or were subjected to great and overwhelming calamities on account of the hope of the resurrection, is equally clear. This interpretation, also, agrees with the general tenor of the argument; and is an argument for the resurrection. And it implies that this was the full and constant belief of all who endured these trials, that there would be a resurrection of the dead. The argument would be, that they should be slow to adopt an opinion which would imply that all their sufferings were endured for nothing, and that God had supported them in this in vain; that God had plunged them into all these sorrows, and had sustained them in them only to disappoint them. That this view is plausible, and that it suits the strain of remark in the following verses, is evident. But there are objections to it:
(a) It is not the usual and natural meaning of the word "baptize."
(b) A metaphorical use of a word should not be resorted to unless necessary.
(c) The literal meaning of the word here will as well meet the design of the apostle as the metaphorical.
(d) This interpretation does not relieve us from any of the difficulties in regard to the phrase "for the dead;" and,
continued...