The verse, in context, read as follows:
"Now, brothers and sisters, I want to remind you of the gospel I preached to you, which you received and on which you have taken your stand. By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain."
- 1 Cor. 15:1-2 (Emphasis added)Paul is quick to make note here that receiving and standing upon the Gospel is not enough. You can listen to the Gospel as much as you want, but it doesn't make you a Christian, he is saying. You can choose to live your life by Christian principles and believe in the historicity of Christ, but that doesn't make you a Christian. You can identify with the church and push for the moral establishment that comes with it, but that doesn't make you a Christian.
All of that, Paul says, is vanity, emptiness, nothingness, a waste of breath. If that is all you believe about Christ, if that is all you consider to be Christianity, then you have believed in mere smoke.
What, then, does true belief that brings about salvation consist of?
I means listening to the Gospel and internalising it, making it a part of your everyday being. It means living your life at the footsteps of Christ, believing in the deity of Christ. It means identifying with the church, standing in solidarity with persecuted brothers and sisters, withstanding persecution yourself and, yet, with grace and forgiveness, loving the world whose morals are so far from Christ as the East is from the West.
A faith that saves is one that, as Paul writes, holds firmly to the Gospel, never wavering or compromising in belief, no matter what storms may come.