I love Advent for several reasons! They include getting ready for Christmas, the excellent advent hymns and carols that we get to sing (we of course sang Let All Mortal Flesh this past Sunday, even though I didn't choose it—it brought tears to my eyes), my anniversary falls during Advent, and I am always reminded by the beginning and ending of the church year of the sonata-allegro form.
The sonata form, you ask? Or, even if you don't, I'll tell you anyway. The sonata-allegro form grew out of simpler forms of music (notably the rounded binary form) during the classical period, and is notable for three main sections—the exposition, the development, and the recapitulation.
The Exposition is where the main thematic materials of the sonata are given. It is usually made up of two themes joined by some transition material and followed by a coda.
The Development takes the themes presented in the exposition and plays around with them, taking them through all manner of different keys and various compositional techniques. It ends with a half cadence (I don't really want to go into that here), to bring back the themes from the exposition.
These themes reappear in the Recapitulation, in which the themes from the exposition are again presented, often in a similar fashion, but most often both in the same, tonic key.
If you're asking yourself, "How does this bear on Advent," here's how: the Christian year, from Advent, to Easter, and back to Advent, follows much the same shape. Advent is not only the time of looking to Christ's first coming, but it's also the time of looking to His second. As the beginning of the Christian year, looking for Christ's first coming sets out the first theme, which continues through Christmas. Advent is also a time of fasting (or not, today—it's traditionally been) in preparation for the feast of Christmas and the days following through Epiphany.
Similarly, Lent prepares for the second great theme of the year, Easter. After Easter and Pentecost, the ordinary time builds on the themes of Christmas and Easter—a time of development. Finally, two weeks before Advent again approaches, readings from the lectionary focus on the second coming—a fitting end to the year, which also brings to mind the first coming, and recapitulating the things that began the year.
Even the ratios of the different times of the year fall into ratios that are similar to those often used in sonata-allegro and other forms. In some years, notably those in which Easter falls between April 17-23 (which will next occur in 2014), the ratio of the days from the beginning of Advent to Easter and Easter to the end of the Christian year is near to 140/225, which, if you're up on your math, is almost exactly the Golden Ratio, used in artistic endeavors since ancient Greece.
So, as a new church year begins, listen to some Beethoven or some Haydn, think about the beauty inherent in the form of the music, and the beauty similarly there in the Christian year, and enjoy them both!