My agent has a non-fiction proposal I wrote for a book called Celtic Song. He didn't get any takers so he's holding on to it for a "better time." But I'm hopeful it will be published one day. (Agent says it's really good, by the way.) ;-)
I'd love for that book to see the light of day because the history of how the Celts used music and song and poetry is colorful and intriguing.
I found this explanation of why hymns should be sung titled "In Praise of Hymnody" in the Irish Liber Hymnorum (or Book of Hymns--pictured above.) Well, I didn't find it in the original. There is a translation online. Wouldn't want to make myself look smarter than I am!
Whoever should recite the hymnody, would be making a song of praise dear to God, for it wipes out all sins, and cleanses the powers of the body and subdues involuntarily the lusts of the flesh; it lessens melancholy, and (banishes) all madness; it breaks down anger, it expels hell’s angels, and gets rid of the devils; it dispels the darkness of the understanding, and increases holiness; it preserves the health, and completes good works, and it lights up a spiritual fire in the heart, ie, the love of God (in place of) the love of man, and it (promotes) peace between the body and the soul.
John Wesley gave this instruction regarding the singing of hymns.
Above all sing spiritually. Have an eye to God in every word you sing. Aim at pleasing him more than yourself, or any other creature. In order to do this attend strictly to the sense of what you sing, and see that your heart is not carried away with the sound, but offered to God continually; so shall your singing be such as the Lord will approve here, and reward you when he cometh in the clouds of heaven.
It's interesting to think about how words, when they are sung, sink into your consciousness, and when they are words of praise, they lift your spirit and echo in your mind long afterward.
Many of the hymns sung in church date from the 18th and 19th centuries. The Liber Hymnorum dates well before that, of course. Many of the hymns the early sang were the Psalms from the Bible. A hymn is an ode or a praise sung to God and could be ancient, more recent, or contemporary. Do you have any favorites?