On the fiftieth day after the resurrection of our Lord and Savior Jesus Christ, the Pentecost day came in which the descent of the Holy Spirit upon the Apostles while they were in Jerusalem.
In that great day we celebrate the octave, which is a feast for salivation offered by the incarnation of our Lord.
Therefore, the church sings for the Lord who ascended into heaven and sent us the spirit of comfort. We worship Him for His glory and passion as He shared our life and never let us orphans for His great love.