The fact that religious devotion can sometimes lead to wondrous things is proven by many composers, from Pérotin all the way to Arvo Pärt. Or it could just be that plainchant, whether derived or original, is universally beautiful.1
Deeply religious music is a tradition still very much alive in both the 20th and 21th century with composers like the aforementioned Arvo Pärt,2 Sofia Gubaidulina and John Tavener.
John Tavener converted to Russian Orthodox Christianity and became heavily involved in mysticism in the 1970s and onwards. A lot of his output consists of large religious works for choir and ensemble or orchestra incorporating religious themes from his studies on mysticism and the Russian Orthodoxy.
One of his most emotionally stunning pieces is “Funeral Ikos” for a small choir, written in 1981. While the piece clearly has a lot of medieval influences, especially when the tenors and basses sing, its harmonies and tone colour would have never been used in those days. There’s emotional tension throughout the sparsely written piece, only fully released by the wonderfully set of Alleluia’s marking the end of each strophe.