Politics and religion often intersect in the United States and many other countries. However, churches generally don't support political candidates (though certain religious leaders do because they're not specifically doing it through the church). There's a reason for that: if they do take on such roles, they have to be taxed.
There are two questions that I am asking. First, why do churches have a tax incentive to not specifically support partisan causes or endorse political candidates? Second, why not tax all churches because of separation of church and state (that religious institutions should not be prioritized over secular ones)?
Note: I use church as a word for any religious institution, not necessarily a Christian one.