There are some people who are considered to be heretics which means that these people are not very keen on religion. They sometimes have beliefs depending on what other people have said. They may not follow what the church says.
The heretics were not allowed to enter the church anymore. They can be considered banned from the church. There were some people and there are still some people right now who are being killed because of their religious beliefs. At that time, the capital punishment which is death was carried out by the Empire. The church can only do so much to punish the people they consider to be heretics.
Only the Empire held the power of the sword (capital punishment). The Church could excommunicate, which meant they could declare someone to be outside the benefits of church and salvation and in danger of eternal separation from God.