Acts 1:8 states, "But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth." This verse is spoken by Jesus Christ to his disciples shortly before his ascension into heaven.
The verse is often interpreted as a commissioning of the disciples to spread the message of Christianity throughout the world, beginning in Jerusalem and extending to all nations.
The phrase "you will receive power" is often understood as referring to the coming of the Holy Spirit at Pentecost, which empowered the disciples to speak in tongues and perform other miracles as they preached the gospel.