First, let us observe this bizarre thought that Paul offered in 1 Corinthians 15: 29. He asked, “else what shall they do which are baptized for the dead…?” It seems that there was a practice in the Corinthian church to baptize living people who stood in proxy for deceased Christians who had not yet been baptized. (Remember that baptism does not save you about is a testimony to what Christ has done for you.) Actually, Paul was dealing with corrupt theology within the church when he asked that question.
Second, this is an important and good example of understanding Scripture. There must be at least one other passage in the Bible that supports the original. In the case of baptism for the dead there was no such support. Nowhere else did the Holy Spirit inspire a writer of Scripture to tell people that baptism was so important they should do it for believers who did not get a chance to be baptized. This false theology is defunct by the example of the penitent thief on the cross. Jesus promised that he would be with him in paradise without any other preconditions. No one else afterwards was baptized in his place for him.
Do not allow people to confuse you over scriptural texts. The teachings of the Bible are uniform and supported by other passages. The central theme of Jesus being prophesied and then fulfilling prophecy for the salvation of mankind runs throughout the Old and the New Testament. In your study of the Bible, make sure you are aware of its content and how it relates to other scriptures.