Gal 1:6 I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel— Gal 1:7 not that there is another one, but there are some who trouble you and want to distort the gospel of Christ. Gal 1:8 But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed. Gal 1:9 As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be accursed.
Paul writes to the Galatians and there are a couple of observations that are important to make in this passage. First there is only one Gospel. This is a great place to bring Mormons. Surely we are in agreement that there is only one Gospel. For the Mormon the challenge is to find their definition of the Gospel in Scripture. This way we use Scripture not just to show them their error but also to show them the Gospel.
Second this is a place where Paul is defining the apostolic succession as it ought to be understood. It wasn’t the office of the apostle that was to be perpetual but the content of the message preached. The Gospel was what determined true apostolic succession. This is an important text to keep in mind when talking with Eastern Orthodox and Roman Catholics who would want to point out apostolic succession.
Third, Paul alludes to the possibility that an apostle could err. “If ‘we’ “speaking of apostles. What is the standard that the apostles are to be measured by? The Gospel. If they aren’t holding to the message of the Gospel and they aren’t preaching Christ then they have demonstrated they aren’t apostolic and that they aren’t in the faith.