Paul has concluded his teaching about the resurrection, sparked by people in Corinth believing false teachers and pagan religionists who said that resurrection did not happen. So Paul explained that the resurrection of Jesus really did happen, and that believers will also be raised to life with a new body when He comes again. The resurrection is an essential part of authentic Christianity: those who deny the resurrection cannot belong to Christ (1 Corinthians 15:1-2).
 
Verse 29 about baptism for the dead is one of the most puzzling in the Bible. It is not a part of Paul's discussion on resurrection. It refers to the practice of 'those' as opposed to 'us' (in v 30), so it is not approved by Paul. It seems to start a little section about those who are ignorant of God and corrupt the character of believers. Some of those people clearly did believe that there is an afterlife with a bodily resurrection and that baptism is a sign of new life in Christ. Those facts were true: but to mix them together by baptising living people to save dead people was wrong. They thought they had found an easy way for people to belong to God … but in fact they had corrupted the apostolic gospel. There is not even a suggestion of such a doctrine anywhere else in the New Testament.
 
Instead, the resurrection motivated the apostles to 'live courageously' for Christ. They knew that they would probably be killed, as Jesus was. They had nothing to lose … death was just the doorway into eternity and their own bodily resurrection when Jesus returns. By contrast, those who thought that 'death is the end' lived for pleasure, satisfying their own desires. Their teaching and example was cancerous to the church. Believers must stay rooted in the Apostles' teaching about the death and resurrection of Jesus, and the expectation of their bodily resurrection when He returns - when each one will give an account of our time spent here. So Paul says, "Come back to your senses as you ought!"
 
The church is still in danger from little additions or subtractions from the gospel. It is not clever to contradict the apostles; their teaching has divine authority. Eventually, false teaching will manifest itself in either wrong behaviour or in futile man-made religious rites, or both. While the true followers of Jesus are living courageously, sometimes risking their own welfare, followers of a false gospel will be seeking power, wealth and pleasure … and will lure others to join them in the hope of an easier life. They do not realise that they will have to give an account to the living Lord Jesus on the final day: everything will be revealed. So if the apostles have not authorised it, forget it! If they command it, do it! Simple!