What always amazes me about this depiction of the scene from Acts 2 is the presence -- even primary presence -- given to Mary, Jesus' mother, and Mary Magdalene. It's rare in Pentecost paintings. Sure, Peter (and later, Paul) led the way in preaching, but women have held a place of primary importance in passing along the faith at least since the Resurrection itself. (NT Wright rightly insists that the place afforded women in the resurrection stories is the best evidence for its historicity.) Acts 1.13-14 even goes so far as to insist that the apostles "were constantly at prayer together, and with them a group of women, including Mary, the mother of Jesus". There's no reason to think Pentecost itself was experience by only the men in the earliest Church, but sadly, that's what most depictions of the event seem to think.
The early Church Fathers found in this story -- as they did in so many passages in the New Testament -- a salvific reversal of an earlier, Old Testament story, namely that of the Tower of Babel. When Babel collapsed, humanity was divided into a multitude of races speaking a multitude of different languages. The pentecostal gift of tongues, allowing the Apostles to preach God's word to all the world, held out the promise of a reunification of humanity, through baptism, within a single blessed Christian community.
That's such a beautiful imagery for the birth of the Church.
I hope you have a blessed Pentecost.
Happy birthday, Church!