Jonathan Farrell/Deuteronomy 16:11

Part of the reason for the feast called Pentecost was for believers to have the opportunity to celebrate and rejoice in God's miraculous intervention within history.  In other words, it was about worship.  The beauty of this is that remembering the testimony (a declaring of what God has done) of Jesus prophesies (declaring what God is going to do) into what He will do among us.  Worshiping God for what He has done creates an atmosphere for miracles.