The birth of Christ is depicted in this window. Angels look on as Mary lays the infant Jesus in the manger.
Notice that each angel is holding at least one white lily. Lilies, often depicted in Christian art and stained glass windows, are a symbol of the resurrection. The bulb is planted in the ground and "dies." But from this bulb comes a new bulb, then stem, leaves and flowers will all rise above the soil. Even though the bulb decays, like the human body, new life springs from it.
Even at Jesus' birth, the shadow of his sacrificial death was already present. Jesus, Son of God, became a human being, living life as we do, then was killed by crucifixion. His earthly body was buried in the ground, and on the third day gloriously rose from the dead.
The angels said to the shepherds in the fields outside of Bethlehem: "For unto you is born this day in the city of David a Savior, who is Christ the Lord. And this shall be a sign unto you: You shall find the babe wrapped in swaddling clothes and lying in a manger." So the shepherds went to Bethlehem to see what the angel told them about, "and there they found Mary and Joseph, and the baby was lying in a manger."
-Luke 2:11-12, 16
The Dalzell Window was presented in memory of James Dalzell (1800-1879) and Martha Duff Dalzell (1807-1879).