"Otherwise, what will they do who are baptized for the dead, if the dead do not rise at all?" (I Cor 15:29). What is "Baptism for the dead"? Could Your Grace please explain this verse?
Baptism for the dead refers to the baptism of the blood through martyrdom. Martyrdom is baptism manifested in the shedding of the blood for the sake of a certain cause which in the case of Christianity, believing in the Lord Jesus Christ. "But Jesus answered and said, "You do not know what you ask. Are you able to drink the cup that I am about to drink, and be baptized with the baptism that I am baptized with?"
They said to Him, "We are able." So He said to them, "You will indeed drink my cup, and be baptized with the baptism that I am baptized with" (Mt 20:22-23) and also "But I have a baptism to be baptized with, and how distressed I am till it is accomplished!" (Luke 12:50).
Many people will accept Baptism with water and Spirit when they see how the martyrs have accepted the Baptism of Blood (martyrdom).
The meaning of “baptized for the dead” is much disputed. The most plausible explanation is that if there were no resurrection of the dead, then those who had undergone all sorts of privations, crosses, severe sufferings, and a violent death just to be baptized and become Christians, would have done that for no reason at all. However, it is the hope in eternity and resurrection with our Lord Jesus Christ that made others want to follow the footsteps of the dead i.e. the martyrs. Going under the water in Baptism, symbolically means dying and resurrecting with our Lord Jesus Christ in eternal life. In the days of the apostles, when unbelievers saw how the martyrs were accepting to die joyfully for our Lord Jesus Christ, they got baptized.