The 52 weeks of the year are broken into two halves for the liturgical church year with each half about 26 weeks in length.
The first half is called the "Life of Christ" and begins with the Old Testament prophecies of the coming Messiah who will break into human history (church season of Advent). Then we celebrate His miraculous birth as the only begotten of the heavenly Father and born of the Virgin Mary. Christ is both God and human (church season of Christmas), His earthly ministry begins as an adult with His baptism in the Jordon River (church season of Epiphany). Then we follow Jesus Christ on the downward way to the cross for 40 days (church season of Lent).
The high point of the entire church year occurs on Easter Sunday and the 40 days Jesus appears to others in His resurrected state before His physical ascension returning to heaven at the right hand of the heavenly Father (church season of Easter).
The second half is called the "Life of the Church" and begins with the Festival of Pentecost. The word "Pentecost" means "fifty days" and occurs 50 days after His resurrection (40 days of Easter + 10 days after His ascension). The church season of Pentecost reveals the work of the Third Person of the Trinity, the Holy Spirit, who calls, gathers, and enlightens the whole Christian church on earth. For approximately 26 weeks or half of the church year we follow the outpouring of the Holy Spirit and expansion and missions of the Christian Church.