V. The coming of Christ in our flesh corresponds with our becoming members of His body
Wherefore since the loving-kindness is manifest, dearly beloved, wherewith all the riches of Divine goodness are showered on us, whose call to eternal life has been assisted not only by the profitable examples of those who went before, but also by the visible and bodily appearing of the Truth Itself, we are bound to keep the day of the Lord's Nativity with no slothful nor carnal joy. And we shall each keep it worthily and thoroughly, if we remember of what Body we are members, and to what a Head we are joined, lest any one as an ill-fitting joint cohere not with the rest of the sacred building.
Consider, dearly beloved and by the illumination of the Holy Spirit thoughtfully bear in mind Who it was that received us into Himself, and that we have received in us: since, as the Lord Jesus became our flesh by being born, so we also became His body by being re-born. Therefore are we both members of Christ, and the temple of the Holy Ghost: and for this reason the blessed Apostle says, “Glorify and carry God in your body:” for while suggesting to us the standard of His own gentleness and humility, He fills us with that power whereby He redeemed us, as the Lord Himself promises: “come unto Me all you who labour and are heavy-laden, and I will refresh you.
Take My yoke upon you and learn of Me, for I am meek and lowly of heart, and you shall find rest to your souls.” Let us then take the yoke, that is not heavy nor irksome, of the Truth that rules us, and let us imitate His humility, to Whose glory we wish to be conformed: He Himself helping us and leading us to His promises, Who, according to His great mercy, is powerful to blot out our sins, and to perfect His gifts in us, Jesus Christ our Lord, Who lives and reigns for ever and ever. Amen.
Source: Sermons (New Advent)