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 under a curse! -Galatians 1:9 BSB
By Paul repeating it twice in verses 8 & 9 (see verse 8 and its commentary), shows the seriousness of the warning—believing in another account of Jesus Christ that goes against or contradicts what the Scripture clearly teaches about the gospels (Matthew, Mark, Luke, and John), will put the individual who accepts it under Divine judgment.
Those who believe it and spread the false gospel will get a higher degree of condemnation from God for deceiving others—taking them away from the Lord.
Two examples of false religions (cults) that teach a false gospel and Jesus are the Mormons & Jehovah’s Witnesses.