It is easy to forget the magnitude of the event of the Nativity of Jesus Christ. This was an act of God akin to Creation itself.
Here is how Saint Gregory the Theologian views it:
Again the darkness is past; again Light is made; again Egypt is punished with darkness; again Israel is enlightened by a pillar. The people that sat in the darkness of ignorance, let it see the Great Light of full knowledge. Old things are passed away, behold all things are become new. The letter gives way, the Spirit comes to the front. The shadows flee away, the Truth comes in upon them. The laws of nature are upset; the world above must be filled. It was an event to give rebirth to all of mankind. It was God's gift so we could return to the union with Him we enjoyed at the time of our creation.
Saint Gregory says,
This is our present Festival; it is this which we are celebrating, the Coming of God to Man, that we might go forth, or rather (for this is the more proper expression) that we might go back to God -that putting off the old man, we might put on the New; and that as we died in Adam, so we might live in Christ, being born with Christ and crucified with Him and buried with Him and rising with Him. As we prepare for this mystical event we need to be sober, to prepare with prayer and fasting, so we can be appreciative of this gift God has given us and give thanks out of our unrestrained love for God. We need this so we are not distracted from all the noise that surrounds this season.
Saint Gregory says,
Let us not adorn our porches; nor arrange dances, nor decorate the streets; let us not feast the eye, not enchant the ear with music, nor enervate the nostrils with perfume, not prostitute the taste, nor indulge the touch, those roads that are so prone to evil and entrances for sin; let us not be effeminate in clothing soft and flowing, whose beauty consists in its uselessness, nor with the glittering of gems or the sheen of gold or the tricks of colour, belying the beauty of nature, and invented to do despite unto the image of God. Not in rioting and drunkenness, with which are mingled, I know well, chambering and wantonness, since the lessons which evil teachers give are evil. Let us not appraise the bouquet of wines, the kickshaws of cooks, the great expense of unguents; and let us not strive to outdo each other in temperance, and this while others are hungry and in want, who are made of the same clay and in the same manner. Finally he asks us to leap with joy as did John the Baptist in his mother's womb.
Now then I pray you accept His Conception, and leap before Him; if not like John from the womb, yet like David, because of the resting of the Ark. Revere the enrolment of account of which you were written in heaven, and adore the Birth by which you were loosed from the chains of your birth, and honour little Bethlehem, which has led you back to Paradise; and worship the manger through which you, being without sense, was fed by the Word . . . If you are one of those who are as yet unclean and uneatable and unfit for sacrifice, and of the gentile portion, run with the Star, and bear your Gifts with the Magi, gold and frankincense and myrrh, as to a King, and to God, and to One Who is dead for you. With Shepherds glorify Him; with Angels join in chorus; with Archangels sing hymns. Let this Festival be common to the powers in heaven and to the powers upon earth. For I am persuaded that the Heavenly Hosts join in our exultation and keep high Festival with us today . . . because they love men, and they love God ... just like those whom David introduces after the Passion ascending with Christ and coming to meet Him, and bidding one another to lift up the gates. This is the time to focus all our actions on the glorification of God and avoid the degrading commercialization of this most important event for the salvation of mankind. All we do during this time preceding the feast of the Nativity should be to heighten our appreciation of the great gift and glorify Him.
St Gregory the Theologian