In Numbers 6:22-27, God gives a blessing to Moses to give to Aaron and his sons (the priests) to put God's name on them. The "Aaronic Blessing" as it's sometimes called, interestingly uses a metaphor for God's face twice in only a few sentences to highlight that when we are in close proximity with God, when we can "see his face" or His face "shines on us", we are blessed. That blessing is specifically the peace of God and Christ's coming as a small child is the ultimate way we see God smiling towards us and bringing us peace.