Why is Pentecost considered the birth of the church?

Pentecost is considered the birth of the church because it marks the day when the Holy Spirit descended upon the apostles, empowering them to preach the Gospel boldly. This event, described in the Book of Acts, resulted in the conversion of about 3,000 people, signifying the establishment of a community of believers. The outpouring of the Holy Spirit enabled the apostles to spread Christ's teachings, thus initiating the growth and development of the early Christian church.