Today is Septuagesima Sunday, and a new cycle of the liturgical year begins.
From the Roman Missal, 1962:
Second Part Of The Liturgical Year
The Easter Cycle
(Mystery of the Redemption)
I. Season of Lent
The Christmas Cycle celebrates the Mystery of the Incarnation. The Easter Cycle celebrates the Mystery of the Redemption and has the following subdivisions:
1. Season of Lent
3. After Whitsunday
Season of Lent
Introduced by three Sundays (Septuagesima, Sexagesima, and Quinquagesima), the season of Lent begins on Ash Wednesday and ends with the death of Jesus in Passion Week. The struggle between our Lord and Satan ends with the victory of the Saviour at Eastertide. During the period from Septuagesima to Ash Wednesday, the liturgy speaks no more of our greatness but comtemplates the misery of fallen humanity--the fatal consequences of original sin and actual sin--and the sacrifice that God asked from the faithful Melchisedech, symbol of the sacrifice that Jesus brings for the whole of humanity.
In this period we also prepare for the fasting and penance of the season of Lent. The season can be recapitulated with the words of the Preface of Lent:
"Who by this bodily fast dost curb our vices, lift our minds, and bestow strength and rewards." Our souls are slaves of the Devil, flesh and the world. Jesus came into the world, not to be crowned king of the Jews, but to deliver us from this threefold bondage and to restore to us the divine life which we had lost.
The season of Lent ends with Passiontide (from Passion Sunday to Easter). The Judica me...and the Gloria Patri are omitted because the very ancient Masses of Passiontide date from an age before these prayers were added to the Roman Mass. The Liturgy commemorates the sorrowful events of the last week of Jesus' mortal life. On Thursday evening, He had the Last Supper with His Apostles, and on the following day He was crucified on Calvary.
"Who didst establish the salvation of mankind on the tree of the Cross, that whence death came thence also life might arise again, and that we, who were overcome by a tree, by a tree might also overcome."
The struggle between our Lord and Satan ends with the apparent success of Satan on Good Friday. The priests are robed in vestments of mourning, and the whole Church wears an aspect of sadness. But by the sacrifice of Himself, the Son of God triumphs and gloriously comes forth from the sepulchre on Easter morning.