When post 13 introduced the Taliban, I wasn’t aware of the the rule, and now I see how 13 threaded the needle to introduce the word.
why ... penalties for Christians who did not want to be a member of the [Catholic Church]
While such penalties would be impossible in modern (past couple of centuries) America, there is nothing out of the ordinary for religious affiliation being enforced by national laws. That is because in the Middle Ages religion was understood to be the foundation of the state; one professing a different religion than the dominant one was considered a traitor. The modern thinking is that religion is free choice; but the historical thinking was that heresy is treason.
As Protestantism gained acceptance, for example, in parts of Germany and in England, equally brutal laws were put in place against the Catholics. In England, for example, being a Catholic priest was a capital offence.