Pentecost
The event that took place on that day [Pentecost] can therefore have no other meaning than that the Holy Spirit, who also existed before that day and gave many gifts and did great works, now, after Christ’s ascension, began to dwell at Christ’s initiative in the church as in his temple. After the creation and the incarnation, the outpouring of the Holy Spirit is the third great work of God.
Herman Bavinck, John Bolt, and John Vriend, Reformed Dogmatics: Sin and Salvation in Christ, vol. 3 (Grand Rapids, MI: Baker Academic, 2006), 500.