"In celebrating this annual cycle of the mysteries of Christ, Holy Church honors the Blessed Mary, Mother of God, with a special love. She is inseparably linked with the saving work of her Son. In her the Church admires and exalts the most excellent fruit of redemption and joyfully contemplates, as in a faultless image, that which she herself desires and hopes wholly to be." CCC 1171
In today's reading, the Catechism discusses the liturgical year, that is the calendar of when the various feasts are in the Church. The Catechism Compendium summarizes this:
In the liturgical year, the Church celebrates the whole mystery of Christ from his Incarnation to his return in glory. On set days the Church venerates with special love the Blessed Virgin Mary, the Mother of God. The Church also keeps the memorials of saints who lived for Christ, who suffered with him, and who live with him in glory. (#242)
The chief feast is of course Easter, the day of the Resurrection of our Lord, and others connected to it. I like how the Catechism Companion, Vol II puts it:
The Easter Triduum is number one: Holy Thursday, Good Friday, Holy Saturday, and Easter Sunday. Those days are the holiest days of the Church year because Jesus' suffering, death, and resurrection are what saves us. The Eucharist is not only Christ's action: it is Christ himself. What Jesus did on the Cross is the heart of everything. (p. 84)
If you step back and think about it for a moment, that's a lot of vitally important events packed into just four days. The date for Easter was set by the Council of Nicaea I, but over time different ways of calculating it caused a division between East and West, thus making it so we usually celebrate on different days. Fortunately, our different calculating methods are in sync this year so all Christians will celebrate the Resurrection of our Lord & Savior on the same day! Hopefully, this matter will be resolved so we can continue to celebrate on the same day from now on.
We have other feast days throughout the year too, of course. For Christmas, the Epiphany, the Blessed Theotokos, holy saints, etc. Those are important too, but nothing can top the Easter Triduum when we can shout for joy that Christ is risen!
Easter calendar for AD 532-626, Museum of Ravenna Cathedral, Italy