Today is the second Sunday of Advent, the theme of PEACE.
The biblical theme of Christ as peace is much different than the secular adaptations of Christmas peace between men. The biblical theme of peace is instead peace brought about by the atoning sacrifice of Christ, not between men but between fallen man [the created] and God [the Creator].
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Thus the Peace that is ushered in at Christ's birth has two applications:
First, peace between God and hostile enmity from fallen humanity.
Second, peace between Gentiles and Christians ... hostile enmity between fallen men.
The unifying peace that the Son of God preached and exhorted was the peace that required mercy and grace. The unifying peace that the Son of God preached and exhorted was the peace that resulted in reconciliation with the Heavenly Father.
A passage from the Advent reading today clarifies what is Heavenly Peace.
"Mercy and truth are met together; righteousness and peace have kissed each other. Truth shall spring out of the earth; and righteousness shall look down from heaven." [Ps 85:10—11] KJV