According to Paul in First Corinthians 15 there are four reasons why Christians would be the most pitiable people on earth if Jesus is not risen from the dead. Then also those who have fallen asleep in Christ have perished. If in this life only we have hope in Christ, we are of all men the most pitiable. The word futile means helpless, powerless, or ineffective. Our faith in Christ has no effect, no power, no result, if Jesus did not rise from the dead.
Christians believe that in Jesus they have salvation or eternal life.
But that is not true if Jesus didn't rise from the dead, because His guarantee of eternal life is conditioned upon His resurrection. And if He did not rise from the dead, then our faith in Him is futile. Take for example the tragic story of Susan Smith. She took her two small sons, strapped them into their car seats, drove the car into a lake, and then watched the car fill with water, drowning them both. Though her sons had trusted her to take care of them, their faith in their mother proved futile, because she was not trustworthy.