Which event signifies the "birthday of the Church" in Catholic belief?

The event that signifies the "birthday of the Church" in Catholic belief is the first Pentecost. This event, described in the New Testament book of Acts, is when the Holy Spirit descended upon the apostles and other followers of Jesus who were gathered in Jerusalem. This moment marked the beginning of the Church's public mission and the empowerment of the apostles to spread the teachings of Jesus.

During Pentecost, the apostles were filled with the Holy Spirit and began to speak in different languages, enabling them to communicate with a diverse crowd that had gathered in the city for the feast. This miraculous event not only serves as a foundation for the Church's missionary activities but also highlights the role of the Holy Spirit in guiding and inspiring the early Christian community.

In contrast, while the birth of Jesus is a significant event in the faith, it does not directly relate to the establishment of the Church. The writing of the Gospels came later and served to document the life and teachings of Jesus rather than to initiate the Church's mission. Similarly, the ascension of Jesus is crucial as it signifies His return to the Father and further prepares the way for the coming of the Holy Spirit, but it is the Pentecost that truly marks the moment the Church began to exist