I’ve been doing some cursory reading about the Hussites and Protestant reformation and I’m having a hard time wrapping my head around why the doctrine of Transubstantiation became such a controversial issue. Many of the other issues contested by the Protestants such as indulgences, iconoclasm, translating the bible, seizing church property, challenging papal authority, ect., have direct temporal and political consequences so I can understand why there would have been so much debate concerning them.
By contrast Transubstantiation seems like a completely theological problem. I can see why it’s an interesting object of debate for a scholar but is it really the sort of thing that a commoner, nobleman or king would care about? From what I’m reading being publicly for or against it could result in persecution or even execution depending on when and where you were.
First, for Luther it was one of many things that the Catholic had added wrongly through "tradition." His theological opinion wasn't much different, but he arrived there differently than Thomas Aquinas did. Aquinas borrowed Aristotelian language to explain that the "accidents" of the bread and wine remain unchanged (i.e. still looks, feels, smells, tastes like bread/wine), but that the "substance" (the underlying reality) has changed. For Luther, "the Holy Spirit is greater than Aristotle." In other words, communion should be understood in Biblical language, not philosophical language.
Second, in the Catholic Church, because the bread was really 100% Jesus, communion was the absolute focus of the Mass. In fact, Mass could be used synonymously with communion. Luther and the other reformers wanted the preaching to be center. Previously a priest could stumble through a short homily and no one would care as long as they received communion. Theologically for the reformers, the Bible trumped the sacraments. Practically for the reformers, preaching helped spread their message.
Third, there was the issue of the laity not receiving communion as bread and wine, but only bread. Practically this made sense because wine was most expensive than bread and Masses were celebrated several times a day. Theologically this made sense for the Catholics because in their thinking the bread and wine are both 100% Jesus, so you get full grace under even one species. Another fear of theirs was the laity spilling the precious blood.
Fourth, it became wrapped up in the whole thrust of the Reformation. To be Lutheran was to believe in Luther's views, to be Calvinist was to believe in Calvin's views, etc. These became official state religions so deviation was unacceptable in many cases.
Source: Hans Hillerbrand's "The Division of Christendom"