“Glory to God in the highest, and on earth peace among those with whom He is pleased!” - Luke 2:14
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The angels proclaim peace on earth because the great Peacemaker had come. Since Adam fell, the world has been in a state of separation from God. Sin has set man at variance with His Maker. There could be no true peace so long as sin was unforgiven, conscience unsettled, and death unconquered. But now peace was possible, for He had appeared who would make atonement for sin and bring in everlasting righteousness. The birth of Christ was the birth of the Prince of Peace. He came to make peace by the blood of His cross. Peace with God is the first fruit of His coming.
Let us beware of the false notion that peace is a universal privilege. The angels do not proclaim peace to all, but “to those with whom He is pleased.” Peace does not belong to the unconverted and unbelieving. Wherever there is faith in Christ, there is peace with God; but without faith there is none. It is a miserable delusion to talk of peace to those who live in sin and care not for the things of God. The world may cry “peace, peace,” when there is no peace. Only those who believe in Christ are truly reconciled.
Let us prize the peace that Christ brings. Nothing can destroy it. Tribulations may come, persecutions may arise, sickness and sorrow may cause much suffering, but the peace which Christ bestows remains secure. It does not depend on outward circumstances but on the finished work of Christ. He is our peace. He has made peace. He gives peace. He will keep in perfect peace those whose minds are stayed on Him. If we would enjoy this peace daily, we must live near to Christ and rest in His love.
(Taken From Expository Thoughts on the Gospels by JC Ryle)