Complex sentence: Carols gained in popularity after the Reformation in the countries where Protestant churches gained prominence (as well-known Reformers like Martin Luther authored carols and encouraged their use in worship), this was the consequence of the fact that the Lutheran reformation warmly welcomed music.
Split into simpler sentences: Carols gained in popularity after the Reformation in the countries where Protestant churches gained prominence (as well-known Reformers like Martin Luther authored carols and encouraged their use in worship). This was a consequence of the fact that the Lutheran reformation warmly welcomed music.