After he gives a list of eyewitnesses to the resurrection of Jesus, Paul states clearly: the resurrection is the basis for the faith of the Christian (15:12-14). Paul says if Jesus Christ is not raised from the dead, our faith is useless. Paul’s point is that is Jesus was not raised, then it is rather stupid to believe Christianity. The world for “useless” here is “without content, without any basis, without truth, without power, empty words….”
Without a resurrected Jesus Christ, Christianity is the same as any other world religion with a dead founder. If there is no risen Lord, then we have a religion, not a relationship. This is the earliest written reference to the resurrection. The gospels and Acts are written as many as ten to fifteen years later even in the more conservative dating of those books. This is important because the belief Jesus was raised from the dead was present from the earliest days of Christianity. This is not a doctrine that developed over fifty or a hundred years.
If the resurrection is not a fact, then the preaching of the Gospel itself is false and those who believe the resurrection are pitiable (15:15-16). It is remarkable that the first witnesses to the resurrection described Jesus as “raised from the dead.” This is not the way a first century Jew would have expected to happen to Jesus even if they thought he was a great teacher or true prophet.
Based on the belief that Enoch and Elijah were translated from life into heaven, it would have been far more natural for the first disciples to describe what happened to Jesus as an ascension into heaven rather than a real death and a real resurrection. The fact that the first witnesses immediately understood that Jesus was really raised is likely based on the fact of his death. He was really quite dead, unlike Enoch (who was translated) and Elijah (who ascended in a fiery chariot seen by eyewitnesses).
Paul takes the argument further in the next few verses: If Jesus is still dead, then you are still in your sins (15:17-19). If there is no resurrection of Jesus, then the Christian faith is futile. If there is no resurrection, then Jesus is still dead. In the preaching of the earliest apostles, the resurrection serves as a proof Jesus was innocent. God vindicated Jesus by raising him from the dead. In Philippians 2:5-11, because Jesus was obedient and humble to death on the cross God raised him from the dead and set him at the very highest place in the universe, God’s right hand, and even knee will bow, and tongue confess that Jesus is Lord. If Jesus was not raised, then he has the status of a very good human teacher and is not at all the Lord of all creation.
If there is no resurrection of Jesus, dead believers have perished. It is likely some members of the Corinthian church had died. If there is no resurrection, then the dead are simply that, dead. If there is simply no resurrection, then even Jesus is still dead, something that is not possible according to the many witnesses Paul listed in the previous paragraph. This might be a kind of logical argument, although the reverse of what might be accepted today.
If there is no resurrection of Jesus, there is no hope in this life and Christians are most pitiable. Paul ties hope to his belief in the resurrection in several passages (1 Thess 4:13, he does not want the readers to grieve like the pagans who “have no hope”). To be pitied (ἐλεεινός) is to be in the most pathetic condition imaginable.