Enmity with God is the source of all that poisons man; overcoming this enmity is the basic condition for peace in the world. Only the man who is reconciled with God can also be reconciled and in harmony with himself, and only the man who is reconciled with God himself can establish peace around him and throughout the world.
But the political context that emerges from Luke’s infancy narrative as well as in Matthew’s Beatitudes indicates the full scope of these words. That there be peace on earth (cf Lk. 2:14) is the will of God and, for that reason, it is a task given to man as well.
The Christian knows that lasting peace is connected with men abiding in God’s eudokia, his “good pleasure.” The struggle to abide in peace with God is an indispensable part of the struggle for “peace on earth”; the former is the source of the criteria and the energy for the latter.
When men lose sight of God, peace disintegrates and violence proliferates to a formerly unimaginable degree of cruelty. This we see only too clearly today.
Joseph Ratzinger, Jesus of Nazareth