Pentecost marks the end of the 50-day Easter season for Christians and falls on Sunday, May 24 in 2015. History The second chapter of the Book of Acts in the Bible's New Testament provides the context for Christian Pentecost. The narrative describes the Holy Spirit descending to a group of followers who, upon receiving it, begin speaking in tongues: "And when the day of Pentecost was fully come, they were all with one accord in one place.