May 19 will be observed by part of the Christian church as Pentecost.
While the kingdom of God is one body, and has existed in all eras of human history, the pouring out of the Holy Spirit upon the church certainly marks the beginning of our current period of mission and ministry.
If one chooses to mark Christmas and Easter, it would seem that recognising Pentecost is helpful in remembering our response to why Jesus came and what he has done for us.
Paul Clark Jr writes some more about corporate worship and Pentecost here.
Even if this is not the pastor’s sermon topic planned for this coming Sunday, I would encourage prayerful attention to opportunities for the church to engage in recognition of the Spirit’s coming to the Apostles as they met (Acts 2), the need for His Holy Presence among us every time we gather, and the glorious mystery of His evidenced work in and among us when we worship around the WORD and TABLE, as well as in our mission. The hymn says it well, “All is vain unless the Spirit of the Holy One comes down.”
He also includes this song from Keith and Kristyn Getty, which is very relevant.