Prior to his ascension to heaven Jesus promised his disciples, "You will receive power when the Holy Spirit has come upon you, ..." The events of Pentecost are seen as fulfillment of this promise.
A strong wind blew and something like "tongues of fire" spread out and touched every person present. Both the wind and the fire are manifestations of God’s spiritual presence, and both are evident in this panel. The expressions on the faces of the representative figures reveal both awe and bewilderment at the strange events.
At Pentecost, the believers became empowered persons -- a new creation, called to proclaim to the world a new kind of life whose signature is love, and grace, and peace, and joy, and faithfulness. At Pentecost, God empowered those who claimed the name of Christ to be channels of the Spirit -- and thus the Christian Church was born in human history.