Advent - its place in creation and in our daily lives as we begin reliving the life of Christ through the Ecclesiastical Year of the Church.
The Jews of old used to observe a number of feasts besides the Sabbath in commemoration of important events in their history (the festival of Easter in memory of the exit from Egypt; Pentecost, in memory of the giving of the law on Sinai; the feast of Tabernacles in memory of their journey through the desert, etc). The Church does much the same; she annually recalls events in Our Lord's life on earth, representing them as vividly as is possible after so long a lapse of time.
The Ecclesiastical Year is an annual commemoration and representation of the life of Christ, and of the time before and after His birth. They are composed of three great feasts: Christmas, when the birth of Christ is celebrated; Easter, the day of His resurrection; and Pentecost, when the coming of the Holy Spirit is commemorated. Each feast has a season of preparation preceding it as well as a subsequent commemoration.
Advent is the season of preparation before Christmas. In the subsequent period we have the feast of the Circumcision, the Epiphany, the Purification, and the Sundays after the Epiphany. This composes the Christmas Season, the first of three seasons commemorating Christ during our annual life as Catholics.
Because Catholicism is a direct lineage from the Jews, the Church commemorates important events in the history of the New Covenant - the Church - beginning with Christ's conception in the womb. The Church places these events before us in order that we may meditate upon them and imitate Our Lord's life. The 3 season cycle is repeated year after year until the end of our Christian lives to draw the soul in deeper intimacy with our Jesus.
In Advent we are called upon to anticipate with the patriarchs of the Old Testament, the coming of the long-expected Redeemer; at Christmas we rejoice with the shepherds at His birth. The four weeks of Advent represent the four thousand years during which the coming of the Messias was expected. The Immaculate Conception occurs most suitably in Advent, the eighth of December, for at the birth of Christ the Sun of justice rose upon the world, dispelling the darkness of sin and ignorance; Mary haralding the coming day of the Lord. The period after Christmas symbolizes the youth of Our Lord, and the time before His entry upon His public ministry - His hidden life at Nazareth.
The aspect of nature corresponds to the three principal festivals: In Advent, the nights are longer than the days, and the life of vegetation is at a standstill; so it was in the spiritual order before the coming of Christ. After Christmas the days begin to lengthen; just so the birth of Christ brought light to the world. At Easter nature awakens to new life and decks herself with verdure; Christ rises glorious from the dead. At Pentecost trees and meadows are in their full beauty of leaf and blossom; with the coming of the Holy Spirit a fresh area commences for mankind, and fair flowers of holiness are brought forth.
And so begins the Ecclesiastical Year - the Catholic representation of the life of Christ for God's greater glory and our spiritual union with our Divine Savior.
Source: Rev. Spirago, Francis; Rev. Clarke, Richard F. S.J. 1899. The Catechism Explained - An Exhaustive Exposition of the Catholic Religion; p. 359-361.