Final answer:
After Jesus' ascension, the apostles experienced the descent of the Holy Spirit on the day of Pentecost, allowing them to speak in various languages and spread Christianity.
Step-by-step explanation:
In chapter 2 of the Acts of the Apostles, shortly after the ascension of Jesus, the apostles were filled with the Holy Spirit during the day of Pentecost.
The descent of the Holy Spirit is described as tongues of fire that enabled the apostles to speak in different languages, allowing them to spread the teachings of Jesus to various ethnic groups and regions.
This event is significant as it symbolizes the birth of the Christian church and the beginning of the apostles' mission to proclaim the crucified and risen Christ to the world.