The Annunciation by Paolo de Matteis, 1712AD.
Ad te levavi animam meam. To Thee have I lifted up my soul. (Introit of the First Sunday in Advent, Ps. 24:1)
Much could be said of the season of preparation for the high feast of Christmas, when we celebrate the birth of our Divine Lord, Jesus Christ. One might note, initially, that it is not the Christmas season, which begins on 25 December, but a season of preparation, and, dare I suggest it, a modicum of penance.
The introduction to the season of Advent in my hand missal admirably describes this time:
"The liturgical texts used during the four weeks of the season of Advent remind the faithful of the ‘absence of Christ.’ The Collects of Advent do not end with, ‘through our Lord Jesus Christ,’ as during the rest of the year. In a spirit of penance and prayer we await the Mediator, the God-Man, preparing for His coming in the flesh, and also for His second coming as our Judge. The Masses for Advent strike a note of preparation and repentance mingled with joy and hope; hence, although the penitential purple is worn and the Gloria is omitted, the joyous Alleluia is retained. The readings from the Old Testament contained in the Introit, Gradual, offertory, and Communion of the Masses, taken mostly from the prophecies of Isaias and from the Psalms, give eloquent expression to the longing of all nations for a Redeemer. We are impressed by repeated and urgent appeals to the Messias: ‘Come, delay no longer.’ The Lessons from St. Paul urge us to dispose ourselves fittingly for His coming. The Gospels describe the terrors of the last Judgment, the Second Coming, and tell of the preaching of St. John the Baptist ‘to prepare the way of the Lord.’
In Advent, the Greek Church celebrates particularly the ancestors of Our Lord – all the Patriarchs and Prophets of the Old Testament, but especially Abraham, Isaac, and Jacob. The Latin Church also mentions them often in this period. In the Breviary, many texts are taken from Isaias (Introit of the second Sunday, Communion of the Third Sunday).
The idea of Advent is ‘Prepare you for the coming of Christ.’ Therefore the very appeals of the Patriarchs and the Prophets are put in our mouths in Advent. Prepare for the coming of Christ the Redeemer, who comes to prepare us for His Second Coming as Judge.
When the oracles of the Prophets were fulfilled and the Jews awaited the Messias, John the Baptist left the desert and came to the vicinity of the Jordan, bringing a baptism of penance to prepare the souls for the coming of Christ. The world took him to be the Messias, but he replied with the words of Isaias: ‘I am the voice of one crying out in the wilderness: prepare ye the way of the Lord.’
During Advent we make straight for Christ the way to our souls – and behold, our Lord will come at Christmas.”
Remarks are abstracted from The Daily Missal and Liturgical Manual, from Editio Typica of the Roman Missal and Breviary, 1962
(Baronius Press Limited, London, 2004, in conjunction with the Fraternal Society of St. Peter, www.baroniuspress.com)"
So, this is a season of longing, and preparing for, the coming of the Saviour -- both more immediately at Christmas, at the end of our own lives, and more remotely, at the end of the world with His second coming.
This link gives you some contemporary directives on the observance of the season of Advent: USCCB: Liturgical Notes for Advent
This article gives some more of the history and context of this great season: Old Catholic Encyclopedia: Advent
This link will take you to a delightful page featuring some customs and observances traditional to the Advent season: Fisheaters: Advent
Here, at the same site, is a bit more about the custom of Advent wreathes: Fisheaters: Advent Wreath & Candles
I close with one of the great hymns of this season, Creator alme siderum, Creator of the Stars of Night, which I present here; first its text, then a recording:
|1||Creátor álme síderum,|
Aetérna lux credéntium,
Jésu, Redémptor ómnium,
Inténde vótis súpplicum.
|Creator of the starry skies! / Eternal Light of all who live! / Jesus, Redeemer of mankind! / An ear to Thy poor suppliants give.|
|2||Qui daémonis ne fráudibus|
Períret órbis, ímpetu
Amóris áctus, lánguidi
Múndi medéla fáctus es.
|When man was sunk in sin and death, / Lost in the depth of Satan's snare, / Love brought Thee down to cure our ills, / By taking of those ills a share.|
|3||Commúne qui múndi néfas|
Ut expiáres, ad crúcem
E Vírginis sacrário
Intácta pródis víctima.
|Thou, for the sake of guilty men, / Causing Thine own pure blood to flow, / Didst issue from Thy virgin shrine / And to the corss a Victim go.|
|4||Cújus potéstas glóriæ,|
Noménque cum prímum sónat,
Et caélites et ínferi
Treménte curvántur génu.
|So great the glory of Thy might, / If we but chance Thy name to sound / At once all heaven and hell unite / In bending low with awe profound.|
|5||Te deprecámur, últimæ|
Mágnum diéi Júdicem,
Armis supérnæ grátiæ
Defénde nos ab hóstibus.
|Great Judge of all! in that last day / When friends shall fail and foes combine, / Be present then with us, we pray, / To guard us with Thine arm divine.|
|6||Vírtus, hónor, laus, glória,|
Déo Pátri cum Fílio,
Sáncto simul Paráclito,
In sæculórum saécula.
|To God the Father, and the Son, / All praise and power and glory be: / With Thee, O holy Comforter! / Henceforth through all eternity.|
Here is the plainchant version of that hymn: