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.
question: what constitutes another gospel? is it that they preach something other than Christ crucified risen and coming again or does it involve more?

1Jn 5:20 And we know that the Son of God is come, and hath given us an understanding, that we may know him that is true, and we are in him that is true, even in his Son Jesus Christ. This is the true God, and eternal life.