Thou didst give a pledge of the general resurrection before Thy Passion, O Christ our God, by raising Lazarus from the dead. Therefore, we too, like the children, carry the symbols of victory and cry to Thee, the Vanquisher of death: Hosanna in the Heights! Blessed is He Who comes in the Name of the Lord.
Lazarus Saturday is a paschal celebration. It is the only time in the entire Church Year that the resurrection service of Sunday is celebrated on another day. At the Liturgy of Lazarus Saturday, the Church glorifies Christ as “the Resurrection and the Life” who by raising Lazarus has confirmed the universal resurrection of mankind even before His own suffering and death.
At the Divine Liturgy of Lazarus Saturday, the baptismal verse from Galatians (“As many as have been baptized into Christ have put on Christ” Galatians 32:27) replaces the Thrice-Holy Hymn, thus indicating the resurrectional character of the celebration, and the fact that Lazarus Saturday was once among the few great baptismal days in the Orthodox Church Year.
Because of the resurrection of Lazarus from the dead, Christ was hailed by the masses as the long-expected Messiah-King of Israel. Thus, in fulfillment of the prophecies of the Old Testament, he entered Jerusalem, the City of the King, riding on the colt of an ass (Zechariah 9:9; John 12:12) the crowds greeting him with waving branches and shouts of praise: Hosanna! Blessed is He Who comes in the name of the Lord! The Son of David! The King of Israel! Because of this glorification by the people, the Jewish priests and scribes were finally driven “to destroy Him, to put Him to death.” (Luke 19:47; John 11:53, 12:10)
Taken from The Orthodox Faith, Vol. II: Worship, by Fr. Thomas Hopko.