Dominus dixit is the introit for the Midnight Mass. The text is a statement from God the Father that Jesus Christ is His Son, forever begotten in the one day of eternity.
Laetabundus is a poetic piece sung before the Gospel at all three Christmas Masses. It is a celebration of the incarnation of the Son of God in the womb of the Virgin Mary, as well as our profession of faith in those mysteries.
Puer natus is the introit for the Mass celebrated on Christmas Day. It speaks of the newborn Child Whose power shall be upon His shoulder, Whose name shall be the Angel of Great Counsel.