Failure to adhere to the official cult of the state has long been punished by death...even back to pagan times (e.g. Socrates, the early Christians etc.)
When Christianity took over in Europe, this old tenet of Roman law was retained. But note: the STATE was doing the executing...not the Church.
Rulers began to abuse this power and were trumping up charges of heresy for political purposes (Joan of Arc’s execution was a classic example).
The Church then said no way...*you*, King or Duke, do not get to decide who is a heretic or not. That is the Church’s job. So WE will take over the fact-finding part of the case...and then we will issue the state a recommendation: execution, or pardon, or whatever.
That, patriot, is why the Inquisition came from. And it is why the records of the Inquisition end with things like “and he was turned over the secular arm to be burned”. But note it was the secular governments that were doing the burning, not the Church.
Read reputable medieval historians on this. I can recommend Jeffrey Burton Russell in particular.
Same evil atrocities, different day