What does Acts 2:1 mean?Just before Jesus ascended into heaven, He told His followers to stay in Jerusalem and wait for the Holy Spirit (Acts 1:4–5). The eleven remaining apostles, along with the women who were so important to Jesus' ministry, Jesus' mother Mary, Jesus' brothers, and dozens of others, settle into the upper room of a house to pray and confer (Acts 1:12–15). For about nine days, they have little to do but praise God (Luke 24:52–53) and choose a successor to Judas (Acts 1:12–26). It's likely they are in this room when Acts 2 opens.
"All together" is from the Greek root word homou, related to the term homothymadon, translated "one accord" in Acts 1:14. Literally, it may mean "together in a group," but spiritually it refers to many individuals working together harmoniously. This attitude will characterize the church in Jerusalem for years to come. They will face many challenges including persecution (Acts 8:1), opposition from within (Acts 11:1–18; 21:17–24), and the inclusion of Gentiles who do not have the Jewish background the founding apostles do (Acts 15:1–35). In all these things, the leaders of the church of Jerusalem strive to maintain a unified front as they seek guidance from the Holy Spirit.
"Pentecost" is derived from the Greek word for "fiftieth." It falls seven weeks and one day—fifty days—after the sabbath that occurs during the weeklong Feast of Unleavened Bread. Pentecost is also called the "Feast of Weeks" because that same period is seven weeks or "a week of weeks." After Passover, Pentecost is the next major feast for which Jews from all over the Roman Empire will come to Jerusalem. It is given in the Mosaic Law in Leviticus 23:15–21 and Deuteronomy 16:9–12.
The Feast of Weeks is the second of three feasts that include a firstfruits offering. When people came to Jerusalem for Pentecost, they were to bring the first of their grain as a free-will offering. On this Pentecost, Jerusalem offers a kind of free-will offering to God as three thousand people believe in Jesus (Acts 2:41).