Such vehement intolerance!

"The doctrine of the death of Christ and its significance was not St. Paul’s theology, it was his gospel. It was all he had to preach. It is with it in his mind — immediately after the mention of our Lord Jesus Christ, who gave Himself for our sins, that He might deliver us from this present world with all its evils — that he says to the Galatians:

'Though we or an angel from heaven preach a gospel to you contravening the gospel which we preached, let him be anathema. As we have said before, so say I now again, if any man is preaching a gospel to you contravening what you received, let him be anathema’ (Galatians 1: 4, 8 f.).

I cannot agree with those who disparage this, or affect to forgive it, as the unhappy beginning
of religious intolerance. Neither the Old Testament nor the New Testament has any conception of a religion without this intolerance. The first commandment is, ‘Thou shalt have none other gods beside Me,’ and that is the foundation of the true religion. As there is only one God, so there can be only one gospel. If God has really done something in Christ on which the salvation of the world depends, and if He has made it known, then it is a Christian duty to be intolerant of everything which ignores, denies, or explains it away. The man who perverts it is the worst enemy of God and men; and it is not bad temper or narrow mindedness in St. Paul which explains this vehement language, it is the jealousy of God which has kindled in a soul redeemed by the death of Christ a corresponding jealousy for the Savior."

From Denney's The Death of Christ.