3...Christ died for our sins, just as the Scriptures said. 4 He was buried, and he was raised from the dead on the third day, just as the Scriptures said. 5 He was seen by Peter and then by the Twelve. 6 After that, he was seen by more than 500 of his followers at one time, most of whom are still alive, though some have died. 7 Then he was seen by James and later by all the apostles. 8 Last of all, as though I had been born at the wrong time, I also saw him. --1 Corinthians 15:3-8
And assuming that Christ has not been raised, your faith is futile. You are still in your sins. --1 Corinthians 15: 17
But there were people in Corinth, and there are still some today, who believe that there is no resurrection of the dead. Paul, in his first letter to the Corinthians (chapter 15), rebutted them plainly and clearly:
20 But in fact, Christ has been raised from the dead. He is the first of a great harvest of all who have died.
21 So you see, just as death came into the world through a man, now the resurrection from the dead has begun through another man. 22 Just as everyone dies because we all belong to Adam, everyone who belongs to Christ will be given new life. 23 But there is an order to this resurrection: Christ was raised as the first of the harvest; then all who belong to Christ will be raised when he comes back.
...many false prophets are gone out into the world. In this you know experientially the Spirit of God. Every spirit who agrees [to the doctrinal statement] that Jesus Christ has come in the sphere of the flesh [i.e., in incarnation] and still remain incarnate [in human form] is of God; and every spirit who does not confess this aforementioned Jesus is not of God. And this is the spirit of the Antichrist...
"Remain incarnate" means that the Lord is in heaven with His human body, the same body that he took when He came on earth through the virgin Mary.
Still, there are some cults who use verse 29 to say that people should be baptized to save their dead ones who were not saved before they died.
29 If the dead will not be raised, what point is there in people being baptized for those who are dead? Why do it unless the dead will someday rise again?
Being baptized like the dead believers, it is proclaiming that we believe the same thing they believed. They believed about the resurrection. They believed that grave is not the end of it all. Our baptism shows our hope that there will be life after death. We believe that the dead believers are gone but not lost. If we did not believe in the resurrection, we would stop getting baptized. But knowing that the dead body would come back alive, we still replace those who are gone by continuing the practice of baptism. We associate with them while waiting for the resurrection of the body.
The Lord promises us bodies that will never die--heavenly immortal bodies. Now, we have the frail earthly body, but when are bodies are transformed and the nature of sin gone, we will be in His likeness. Amen.
49 Just as we are now like the earthly man, we will someday be like the heavenly man.