The Christian Calendar

the calendar; image from here

Happy Easter!  Today seems suitable to present the Christian calendar. Everyone knows about Christmas and Easter, but there's far more to it.  "The Christian calendar is an annual schedule that commemorates certain days and seasons related to the history of salvation." (from the Gospel Coalition)

The above image shows the main events in the year.  More explanation follows; I'm indebted to the aforementioned Gospel Coalition link for any quotes (and the general structure of) below.

• Advent
• The start of the Christian liturgical year
• Begins on the fourth Sunday before Christmas
• We anticipate the arrival of our Savior, Jesus Christ, on Earth
• Christmas
• Begins on 25 December and lasts 12 days (until 5 January)
• We celebrate Christ's birth
• Epiphany
• Means manifestation
• Begins when, according to tradition, the magi visit the Christ
• We celebrate the revelation of Jesus as God incarnate to the entire world (Jewish and Gentile)
• Lent
• Begins on Ash Wednesday, lasts 40 days (not counting Sundays) until Holy Saturday
• "The period represents the forty days Jesus spent in the wilderness, enduring the temptation of Satan and preparing to begin his ministry."
• We examine ourselves and repent
• Holy week is the last week of lent and leads us to Easter.  Holy week includes 
• Palm Sunday (Jesus' entry into Jerusalem), 
• Maundy Thursday (the Last Supper), 
• Good Friday (His crucifixion), and
• Holy Saturday
• Easter
• Commemorates Jesus' resurrection from the dead
• Lasts 40 days (the length of Jesus' time on Earth following His resurrection), ending with Ascension Thursday, when He returned to Heaven
• Pentecost
• Commemorates the Holy Spirit coming
• Is 10 days after Ascension Thursday, or 50 days after Easter
• Ordinary Time
• Though there's no special celebration during these months, we're commanded to always rejoice (Philippians 4:4) and follow Jesus, seeking to love Him and our neighbors, which is the sum of the law (Matthew 22:35-40)

Why do we celebrate annually?  Because we're called to remember, and we need reminders- constantly- of who God is, what He has done, who we are, what we need, and how Jesus loves us.