The Catholic Defender: Peace with God is His best gift to man, From a Sermon by Saint Leo the Great, Pope

The Saviour then, dearly beloved, is born not of fleshly seed but of the Holy Spirit, in such wise that the condemnation of the first transgression did not touch Him.

And hence the very greatness of the boon conferred demands of us reverence worthy of its splendour.

For, as the blessed Apostle teaches, we have received not the spirit of this world but the Spirit which is of God, that we may know the things which are given us by God 1 Corinthians 2:12: and that Spirit can in no other way be rightly worshipped, except by offering Him that which we received from Him.

But in the treasures of the Lord's bounty what can we find so suitable to the honour of the present feast as the peace, which at the Lord's nativity was first proclaimed by the angel-choir?

For that it is which brings forth the sons of God, the nurse of love and the mother of unity: the rest of the blessed and our eternal home; whose proper work and special office it is to join to God those whom it removes from the world.

Whence the Apostle incites us to this good end, in saying, being justified therefore by faith let us have peace towards God Romans 5:1 .

In which brief sentence are summed up nearly all the commandments; for where true peace is, there can be no lack of virtue.

But what is it, dearly beloved, to have peace towards God, except to wish what He bids, and not to wish what He forbids?

For if human friendships seek out equality of soul and similarity of desires, and difference of habits can never attain to full harmony, how will he be partaker of divine peace, who is pleased with what displeases God and desires to get delight from what he knows to be offensive to God?

That is not the spirit of the sons of God; such wisdom is not acceptable to the noble family of the adopted.

That chosen and royal race must live up to the dignity of its regeneration, must love what the Father loves, and in nought disagree with its Maker, lest the Lord should again say: I have begotten and raised up sons, but they have scorned Me: the ox knows his owner and the ass his master's crib: but Israel has not known Me and My people has not acknowledged Me Isaiah 1:2-3

Revised and edited for New Advent by Kevin Knight