What was the New Life Christ's Birth Brought?

The birth of Jesus, the Incarnation of God, brought to all people a new life. It was a renewal of mankind. This was a cosmic event unparalleled in the history of man. From henceforth the life of man was different

Saint Anthony gives us some insight into this new life.

It is not said in vain, brothers, that Christ brought new lifeto the earth. We see that he turned the human soul around completely; changed itsnature, as it were. Formerly people accumulated wealth, now they have started to give itaway; formerly they feared prisons and torments, now the Apostles exultantly thank Godfor them; formerly they feared afflictions, now St. James writes to the Christians: "Mybrethren, count it all joy when ye fall into divers temptations" (1:2). On earth, as before,there is injustice, and sickness, and poverty, and all kinds of offences, and the moretime passes, the more of this there will be, as the Lord predicted, as well as the HolyApostles Peter, Jude, Paul and John. But the souls of Christians were not overwhelmedor crushed by all these afflictions. They came to know another blessedness -- inner and spiritual -- and if they grieved about anything, then it was only about their falls into sinand the sins of their neighbours.

the Nativity was the beginning of a new life as recorded in the Scriptures of the New Testament. This new life did not begin with a statement of earthly wealth, but began in totally humility and poverty. In Bethlehem God was born as man in a stable. Was this because he could not have been born elsewhere? Of course not. God could have chosen the wealthiest palace if this was what He desired. But He came to bring to earth a divine economy and chose the humblest of places. He came to uplift mankind beyond eartly riches, to enable us to return to a life in His kingdom.
Saint Anthony writes,

Look what happens according to the customs of the new life. He to Whom all thehouses, all the towns, and the whole universe belong, deprives Himself of the lasthuman dwellings and takes up His abode together with beasts, committing Himself to anirrational manger instead of the throne of cherubim. O people! Is it for you to struggleand torment each other for preference in honor, cleanliness and comfort, when Goddoes not spurn not being allowed in to where people are and is satisfied with an animalshed! Man! You murmured about your poverty, you looked with an envious eye on therich and famous, you lamented the poverty of your own hut, your grieved that you areaccounted as one of the simple folk. Go down yet lower in your station in life, and youwill be accounted to be with God! You considered it a great honour to approach thedoorstep of a lord, but look how easily you can obtain a dwelling equal to God's house.You look at palaces with desire, ! because kings live in them or have lived in them; lookrather at the stall where the incarnate Son of God dwelt. You see where is the beginningof the new teaching, of the new life, of the new customs. If you follow after Christ in thisway, no place will be crowded for you. If everyone takes to heart the image of Christ'slife, then there will be plenty of room and no offence for anyone. 

This new life that was brought by this new Birth was one not according to the desires of this world, but was to welcome us into a home that is much greater, the house of God. God became man so we could rejoin wirth Him in His house. His birth united His divine being with our human being so we could become divine.
So, to what are we called in this new home? Saint Anthony tells us the following:

And so, the new life in Christ consists in willingly renouncing worldly goods and notgrieving when they are taken away by force. Perhaps you cannot direct your mind thisway at once. But to the extent that you willingly deprive yourself of earthly enjoyments,however reluctantly: fast, offend yourself by giving to the poor or giving way to others,do not become angry or take revenge for oppression, but bear offences in silence; -- tothe extent that you crucify the old man in yourself -- to this extent will a new fount ofgrace-filled life flor out of your heart. "He that believeth on Me," says the Lord, "out ofhis belly shall flow rivers of living water: (Jn. 7,38). It is no longer either riches, or health,or glory, or the destruction of enemies that will make you rejoice, but, just as a farmerrejoices over a ripening field, or a hunter over a lot of wild fowl fluttering about, or anartist over the beauty of a sunset -- so you will rejoice over praye! r, spiritual reading andthe opportunity to be kind to your neighbour, either by giving, or consoling one who isgrieving, calming one who is angry, or bringing a villain to his senses. The impious Jewsdid not want to accept this new life: they wanted earthly happiness, and the destructionof enemies, and human glory, and vain riches. It is the same thing which their foolishpupils want even now, Europeans of various nationalities, and many here in Russia.They have forgotten Christ, have come to hate Christ's abasement and love thetreasures of the land of Egypt, not like the great Moses (Heb. 11:26), but "like theancient foolish people in the wilderness."

The celebration of the Nativity is a call to let go of the attachments we have to the pleasures of this world so we can gain a much greater joy. This seems so far removed from how we celebrate this event today. We are busy making our lists, making sure everyone knows the worldly item we most desire in hopes that we might receive it as a gift. We are busy sorting through ads to find the best deals on the many purchases we will make. We are decorating our surroundings with images of Santa, reindeer, snowmen and possibly a few angels, but mostly with worldly symbols. It seems we have forgotten what the day called Christmas is really about.
Saint Anthoy reminds us that this day opens for us a new path to eternal life.

Christ God taught us, brothers, to teach others not to seek for rights,but to renounce them, not to demand equality with the gentry, but self-abasement, not tofight, but to give way, not to commit crimes, but to bear offences. This is how themanifest Sun of Righteousness "hath given us light and understanding" (1 Jn. 5:20), hasopened for us the path to eternal and blessed life; this is what all righteousness inhuman society is based on. 

How are we to celebrate? Rejoice in His glory and the gift we have received to join with God for eternal life in His kingdom. Let us give thanks and glorify God.
Saint Anthony concludes,

Then let us, brothers, glorify the Lord Who has appeared,rejoice! in His Nativity! Nothing will take this joy away from us, -- neither poverty, noroffences, nor labour day and night: He has blessed all this, and magnified it, andsanctified it with Himself in the town of Bethlehem. Let is draw instruction from here, andto Him, Who has loved us, glory and honour, power and worship, with the Father andthe Spirit for ever. Amen.

Reference: SERMON ON THE NATIVITY OF CHRIST by Blessed Metropolitan Anthony, 1906