How did Medieval Catholic Mass evolve to how it is today?

by Dolecto

If I were to attend one, say, in the 14th Century or something, would there be a major difference?

SirHumphreyGCB

Yes. To respond somewhat quickly to you there have been multiple iteration of the "Mass" throughout the history of Catholicism. If we were to isolate two key moments I would undoubtedly say the Council of Trento (1545-1563) and the Second Vatican Council (1962-1965) because they both had a major role in shaping the mass (as the core of any major religious ceremony in catholic liturgy). In particular the Mass that we know today (the series of religious rites culminating in holy communion) as the main spiritual moment is a product of Trento and is therefore often referred to as "Tridentine". It basically tried to overhaul the complex and often devolved ensemble of rites that existed during the middle ages. Of course this was largely on paper until the different dioceses started to give a somewhat uniform education to priests through the seminars system, a feat that would take centuries to reach. The Vatican II basically modernised the blueprint but kept the centrality of the Mass as the main rite. The most known changes were the switch from Latin to "common" in most masses and the "inclusion" of lay parishioners in the rite through service books and such.

So basically you would realistically not have a single "mass" in the XIV century but rather multiple rites (some culminating with communion although relatively rare) that could change between dioceses. One example of diocesan peculiarity is the "Ambrosian Church" of the Archdiocese of Milano.

If you are interested in medieval religious practice I would personally recommend to look into Anglican liturgy since "Anglo-Catholic" or "High church" congregations have a deeper tradition of medieval rites as they were not involved in the Counter-reformation.