Final answer:
On Pentecost, about three thousand people were added to the church after the descent of the Holy Spirit as detailed in the book of Acts 2.
Step-by-step explanation:
On the day that the Holy Spirit descended - a day known as Pentecost - a significant number of people were added to the church. According to the New Testament in the Bible, specifically the book of Acts 2, about three thousand souls were added to their number that day.
This event marked a pivotal moment in the early Christian church as the apostles began to preach and spread the teachings of Jesus Christ widely, empowered by the Holy Spirit, who is said to have descended upon them in the form of tongues of fire.