There are different ways that God talks to us and that we human beings talk, or communicate, with each other. Words are the most common way. Images like paintings, sculptures, etc. also communicate ideas and feelings. But one of the deepest ways to communicate is by using music. When we hear music, even without words or lyrics, we can feel happy, sad, energetic, hopeful, etc.
Why do we react this way to music? Because God created us that way. He uses music to inspire us, influence us, encourage us and more. He also enjoys good music and has always told His people that He wants to be worshipped in ways that include songs. Sometimes the songs have words but devotional music can be just instruments.
This does not mean that all music is good - either for worshipping God or even for us to listen to. Everything that God created is good. But devils and humans on earth can twist or abuse the good that God created until it actually becomes sinful. Music is no exception. Today there is a lot of bad music; some of it is very bad. But God created music to be used properly for a good reason or purpose. When it is, music is wonderful. It lifts our spirits, gladdens our heart and fills our minds with hope and happiness - especially when it inspires us to think about God, or the things of God, like His Most Blessed Mother, Mary.
As Saints learn to conquer their sinfulness and grow in virtue they grow closer to the Most Holy Trinity. As they grow in union with God, they begin to love what He loves and as He loves. For example, they grow to love the Blessed Virgin Mary more than anyone or anything else, except of course for God Himself. Truly good music is one of the things Saints grow to appreciate. Gregorian Chant, for example, is a simple and yet beautiful form of good music that has been used to praise and worship God since the early Church. Not all the Saints react in the same way (or degree) to all forms of good music. But every Saint will recognize something of God Himself present in the beauty, the order, and the harmony of truly good music.
The great Saint Francis of Assisi (1182-1226) was no exception. He was very familiar with the Holy Catholic Bible and had read how the Holy Angels in Heaven and people on earth have used good music many times to express their love and adoration for God. Heavenly music had accompanied some of the most important events in the Holy Bible. We are even told that music has and always will be played in Heaven for the greater honor and glory of God and the delight of Our Lady, and all the inhabitants of Heaven.
One day, when the Saint was troubled about many things, he turned his mind to God and the things of Heaven. Thinking about how wonderful everything is in Heaven, St. Francis realized that, no matter what God might ask him to suffer in this life, the rewards of Heaven were worth infinitely more. To comfort himself in his trials, he reminded himself that in Heaven "There, at least, is eternal peace and happiness!"
Then, he sensed an angel near him with a violin. "Francis," the heavenly messenger sweetly called to him, "I will now play for thee as we play before the throne of God in Heaven!" Then the celestial musician placed the violin to his chin and pulled the bow across the strings - but only once. Immediately, the holy Saint was filled with a great joy and sweetness to the depths of his soul. He felt as though he no longer had a body and that all of his suffering had completely vanished. The next morning, he told his brother Franciscans that "If the angel had drawn the bow across the strings again, my soul would have left my body from the uncontrollable happiness!" Saint Francis would have died of joy. Such is the incredibly beautiful music that God has created to fill us with complete delight if we get to Heaven one day.