I am astonished that you are so quickly deserting the one who called you by the grace of Christ and are turning to a different gospel – which is really no gospel at all. Evidently some people are throwing you into confusion and are trying to pervert the gospel of Christ. But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned! (Gal. 1:6-9)This is a good measuring stick against which we can evaluate what claims to be true. It is the Gospel that saved us. This Gospel is succinctly expressed in 1 Corinthians 15:1-5:
Now, brothers, 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. For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to Peter, and then to the Twelve.