Near the end of Vespers, just before the blessing of the loaves, the choir sings the "Aposticha" hymns.  Anticipation is building to higher and higher levels as we approach the censing of the Icon of the Feast and the singing of the Troparion "Your nativity, O Virgin, has proclaimed joy to the whole universe". 

A theme of the Aposticha Hymns is the great reversal of sadness into joy  --  the change of lamentation into thanksgiving  --  as God, through Mary, for "the life of mankind now dwells in the world."

Let those on earth be decked in splendor;
let rulers leap for joy;
let priests be glad in blessing;
let the whole world keep the feast!