In the letter of St. Paul to the Galatians, it says that those involved with factions will not enter Heaven, so how come being part of the Republican or Democratic party is not mortal sin?
Paul condemns those who would divide the Church. He does not speak of political parties, which did not exist in the Roman Empire.
So this means bad news for protestants and eastern orthodox/byzantine Catholics?
Political parties should not be viewed as divisions within the Church. Within the Church, there’s only one “team”.
Schism is certainly a very grave sin. However, those persons born into protestant or Eastern Orthodox Churches which have been separate for centuries are not themselves necessarily guilty of schism.