On Music, Sound, Affect and Ineffability explores early reflections on music and its effects on the mind and soul. Even if we cannot say precisely what these early theologians heard - only a snippet of an early hymn from that period remai - we can learn how they heard it.
Augustine is an obvious place to start; his De Musica is the only treatise we have on music by a Christian philosopher in the first five centuries. For five of its six books, it considers the classical, liberal discipline of music, concerned with numerical measure and rhythm, but in the sixth book, it opens into considerations of music, perception, and Christianity.
In both it and The Confessions, Augustine establishes a psychology and an ethics of musical perception, which considered together form an effective theology of music. For Augustine, music - both heard and performed - becomes the means by which we can sense and participate in divine grace.