It would seem that before Vatican II (although since when, I cannot tell) there was a penitential character about Advent, and that after Vatican II this character has been obscured or even removed completely in some locales. (Let it be known, though, that at my previous parish, there were two special Reconciliation liturgies — including individual confession — held during the year: one in Lent and one in Advent.) Yet Advent is a time when we prepare for the Lord's second coming (which brings with it the Final Judgment) at the same time that we recall His first coming (which was to save His people from their sins).
I bring this up because a bishop recently wrote the following in his pastoral letter on Advent:
The word advent comes from the Latin for “coming” or “arrival”. What arrival are we waiting for? The General Norms for the Liturgical Year helps us understand the season a little bit better by explaining:What do you think? Is Advent a penitential season? Should it be?
The season of Advent has a twofold character: It is a time of preparation for Christmas when the first coming of God’s Son . . . is recalled. It is also a season when minds are directed by this memorial to Christ’s second coming at the end of time. It is thus a season of joyful and spiritual expectation. (General Norms for the Liturgical Year, 39)You will notice that this is not a penitential season. It is a season of joyful hope, a time of preparation and waiting. “Thus the Sundays of Advent, while commemorating [Christ’s] birth and anticipating his return, celebrate in word and sacrament his coming now in the midst of this world.” (Normand Bonneau, The Sunday Lectionary: Ritual Word, Paschal Shape, Collegeville: Liturgical Press, 1998, 131.) This season is not just about preparing for the birth of Christ at Christmas, but for the Christ who is continually being born in our midst and transforming the Church ever more into his body in the world.
For your edification and education, here is a selection of quotes from magisterial documents from the past century or so about Advent.
In the period of Advent, for instance, the Church arouses in us the consciousness of the sins we have had the misfortune to commit, and urges us, by restraining our desires and practicing voluntary mortification of the body, to recollect ourselves in meditation, and experience a longing desire to return to God who alone can free us by His grace from the stain of sin and from its evil consequences. (1947, Pius XII, Mediator Dei 154)
Accordingly, the playing of the organ, and all other instruments is forbidden for liturgical functions, except Benediction, during the following times: a) Advent, from first Vespers of the first Sunday of Advent until None of the Vigil of Christmas; b) Lent and Passiontide, from Matins of Ash Wednesday until the hymn Gloria in excelsis Deo in the Solemn Mass of the Easter Vigil; c) the September Ember days if the ferial Mass and Office are celebrated; d) in all Offices and Masses of the Dead. (1958, Sacred Congregation of Rites, De Musica Sacra 81)
The playing of these same instruments as solos is not permitted in Advent, Lent, during the Sacred Triduum and in the Offices and Masses of the Dead. (1967, Sacred Congregation of Rites, Musicam Sacram 66)
Advent has a twofold character: as a season to prepare for Christmas when Christ's first coming to us is remembered; as a season when that remembrance directs the mind and heart to await Christ's Second Coming at the end of time. Advent is thus a period for devout and joyful expectation. (1969, General Norms for the Liturgical Year and Calendar 39)
This accentuates the penitential dimension, already present in the Advent season and vividly recalled by the person of John the Baptist, who teaches, precisely, that the way of the Lord is prepared by changing of one's mentality and life (cf. Mt 3: 1-3). (1999, John Paul II, Angelus of 28 November)
During Advent the floral decoration of the altar should be marked by a moderation suited to the character of this season, without expressing prematurely the full joy of the Nativity of the Lord. During Lent it is forbidden for the altar to be decorated with flowers. Laetare Sunday (Fourth Sunday of Lent), Solemnities, and Feasts are exceptions. (2002, GIRM 305)
In Advent the organ and other musical instruments should be used with a moderation that is consistent with the season's character and does not anticipate the full joy of the Nativity of the Lord. (2002, GIRM 313)
Advent is a time of waiting, conversion and of hope: 1) waiting-memory of the first, humble coming of the Lord in our mortal flesh; waiting-supplication for his final, glorious coming as Lord of History and universal Judge; 2) conversion, to which the Liturgy at this time often refers quoting the prophets, especially John the Baptist, "Repent for the kingdom of heaven is at hand" (Mt 3,2); 3) joyful hope that the salvation already accomplished by Christ (cf. Rm 8, 24-25) and the reality of grace in the world, will mature and reach their fulness, thereby granting us what is promised by faith, and "we shall become like him for we shall see him as he really is" (John 3,2). (2002, Directory on Popular Piety and the Liturgy 96)
Popular piety, because of its intuitive understanding of the Christian mystery, can contribute effectively to the conservation of many of the values of Advent, which are not infrequently threatened by the commercialization of Christmas and consumer superficiality. Popular piety perceives that it is impossible to celebrate the Lord's birth except in an atmosphere of sobriety and joyous simplicity and of concern for the poor and marginalized. The expectation of the Lord's birth makes us sensitive to the value of life and the duties to respect and defend it from conception. Popular piety intuitively understands that it is not possible coherently to celebrate the birth of him "who saves his people from their sins" without some effort to overcome sin in one's own life, while waiting vigilantly for Him who will return at the end of time. (2002, Directory on Popular Piety and the Liturgy 105)
If Advent is the season par excellence that invites us to hope in the God-Who-Comes, Lent renews in us the hope in the One who made us pass from death to life. Both are seasons of purification - this is also indicated by the liturgical colour that they have in common... (2008, Benedict XVI, Homily of 6 February)