The prayer to the Holy Spirit...

The prayer to the Holy Spirit, "O Heavenly King", said in almost every Orthodox prayer service is NOT said from Paschal matins (the first service of the Pentecostarion), which begins at midnight on the Sunday of Pascha, until the Vespers service for Pentecost. Anywhere this prayer occurs it is omitted, and until Ascension Thursday, is substituted with the Paschal troparion (Christ is risen from the dead, trampling down death by death, and upon those in the tombs bestowing life), sung three times. We are like the Apostles during this period, "waiting" for the Holy Spirit to come, and the absence of this prayer makes a strong statement of our profound need for the Holy Spirit.