Christmas Time and Easter Time highlight the central mysteries of the Paschal Mystery, namely, the incarnation, death on the cross, resurrection, and ascension of Jesus Christ, and the descent of the Holy Spirit at Pentecost. The Sundays and weeks of Ordinary Time, on the other hand, take us through the life of Christ.
This is the time of conversion. This is living the life of Christ. Ordinary Time is a time for growth and maturation, a time in which the mystery of Christ is called to penetrate ever more deeply into history until all things are finally caught up in Christ. The goal, toward which all of history is directed, is represented by the final Sunday in Ordinary Time, the Solemnity of Our Lord Jesus Christ, King of the Universe. (from USCCB website)
Ordinary Time is called “ordinary” simply because the weeks are numbered. The Latin word ordinalis, which refers to numbers in a series, stems from the Latin word ordo, from which we get the English word order.
Thus, Ordinary Time is in fact the ordered life of the Church. It’s appropriate, therefore, that the Gospel for the Second Sunday of Ordinary Time (which is actually the first Sunday celebrated in Ordinary Time) always features either John the Baptist’s acknowledgment of Christ as the Lamb of God or Christ’s first miracle—the transformation of water into wine at the wedding at Cana.
Thus for Catholics, Ordinary Time is the part of the year in which Christ, the Lamb of God, walks among us and transforms our lives. That’s why there’s nothing “ordinary” about Ordinary Time. (from About Catholicism website)