Look at it this way.
THE DOMINANT AND THE TONIC CHORD
(Harmony lesson #1)
"Music is nothing else but wild sounds civilized into time and tune" says Thomas Fuller. It's true! As magical and mysteriously powerful as it can be, music can be simply broken down into three elements: rhythm, melody, and harmony. Let's explore harmony.
Harmony is the chord underneath that enhances the melody that we sing. It happens when several notes are sounded at any one time. We don't really need harmony to sing a song, but it sure does make it nicer. Think of what it sounds like to sing a hymn without any accompaniment. Melodies are horizontal, harmony is vertical; melodies are like the activities we do everyday; harmony is how we feel about them.
Basically speaking, there are two kinds of harmonic chords: a chord that suggests something more to come and a chord that suggestions completion. The former chord is called the "Dominant" chord, and the latter the "Tonic". I don't know about you, but when I was a child I could hardly make it through December waiting for Christmas morning to arrive. Those 25 days seemed like an eternity. I was excited to the point of distraction waiting in anticipation. This is what the Dominant chord feels like. Composers use the Dominant to create a feeling of anxiety, or anticipation, or hope, or contemplation, etc.. The second chord, the "Tonic", is the sought after resolution to the tension created by the Dominant. It is the answer to the question, the fullfilment of the anticipation, the relaxation of the anxiety, or the hoped for salvation, etc..
In its own significant way, the church through the centuries has evolved a harmony of its very own. It creates a spiritual "dominant" chord when it observes Advent. During Advent, we think about the tension of the end of the world, anticipate the coming of a mighty savior, and renew the hope of a faithful maiden girl. That's why we don't sing Christmas Carols during Advent; because the birth is like the Tonic Chord. Each season of the Liturgical Year (Advent, Christmas, Epiphany, Lent, etc.) has its own blend of chords that is unique and that serves a purpose towards a healthy spirituality. Praise God by the "Tonic"; but first the "Dominant".
During Advent, we think about the tension of the end of the world, anticipate the coming of a mighty savior, and renew the hope of a faithful maiden girl.