Make ready, O Bethlehem; let the manger be prepared, let the cave show its welcome. The Truth is come, the shadow is passed away...(From the First Royal Hour of the Nativity).
It is the Eve of the Nativity when these words are sung. The transformation of the world, the birth of God, is but hours away, and it is through such words that the faithful are called to attentiveness and anticipation.
'Make ready, O Bethlehem.' We can see the radiant lights of the feast just beyond the horizon, we can taste the sweetness of the miracle that took place beneath a star; and through the words chanted in the Church, the coming of the birth of God is made a reality to us. We make ready, and we wait.
Why the Fast?
But this is not the first moment of preparation for the Feast. For forty days the Church has been setting herself in readiness, drawing her attention to the mystery to come, waiting in expectation. In anticipation of the great joy that is to come on Christmas day, she has taken up the task considered by so many as the opposite of joy: fasting, with all its rigor, its harshness, its discomfort. For Orthodox Christians everywhere, the fast is that which leads to the radiant wonder of the Nativity of Christ.
Why do we often feel, that this fast 'stands in the way,' so to speak, of our arrival at Christmas rejoicing? The fast seems awkward because so often we see Christmas as joy alone and do not appreciate fully the deep and profound mystery that is at the heart of our rejoicing. 'Hark, the herald angels sing!' we are eager to remember, but we forget the universal significance of the event that is the cause of the angels’ singing. It is not just that a Babe is born, but He Who is without birth is born. He Who created all things is made a created Child. He Who holds the universe in the palm of His hand, is held in the hands of a tender mother.
Before Thy birth, O Lord, as the noetic hosts looked with trembling on the mystery, they were struck with awe: for Thou Who hast adorned the vault of heaven with stars, wast well pleased to be born as a little babe; and Thou wast laid in a manger of dumb beasts, Who holdest all the uttermost parts of the earth in Thy hand. For by such a dispensation hath Thy compassion been made known, O Christ, our great mercy, glory be to Thee (from the Third Royal Hour).
We do not tremble when we think of Christmas; we are not struck with the wonder of the Nativity. Instead, we buy gifts and plan parties, catching a glimpse of the joy of the Feast, but without a heart immersed in its wonder. Thus the fast becomes something we must 'get through' in order to reach that joyful day. When we arrive there, however, if this has been our attitude, we are spiritually bewildered by the hymns with which the Church fills our hearts. We find ourselves joined to a celebration of triumphal release from bondage, but we little understand what that bondage means. We sing songs of joy for deliverance, but we do not truly comprehend how we are enslaved. We find ourselves suddenly transported to the mountaintop, but unless we have climbed there from the valley far below, the scene we see is only another beautiful picture casually set before our eyes, and not the vision for which we have worked and struggled and longed with all our being. We may feel joy, perhaps even Christmas joy; but we will know, deep inside, that our joy is not like that which is exalted in the hymn:
Be glad, O ye righteous; ye heavens rejoice exceedingly; ye mountains, skip for joy, as Christ is born. Imitating the Cherubim, the Virgin becometh a throne, carrying in her bosom God the Word incarnate. Shepherds glorify Him that is born. Magi offer gifts unto the Master; and Angels sing praises, saying: 'O incomprehensible Lord, glory be to Thee’ (first sticheron of the Praises, Nativity Matins).
An Ascetic Journey
The fast of the Nativity is the Church's wise solace and aid to human infirmity. We are a spiritually forgetful people, but God knows our forgetfulness. We who run afar off from Him are called to return. We who fall far from God through the magnitude of our sins are called nonetheless to be close to Him. Through the fast that precedes the great Feast of the Incarnation, the Church helps draw us into the full mystery of what that call entails.
Like Great Lent, the fast of the Nativity is a journey—a journey toward that salvation first promised to Adam in God's curse laid upon the serpent (Gen 3.14-15). The One who will crush the head of the serpent, of sin and the devil is He to Whom the star leads us.
Come, ye faithful, let us see where Christ the Saviour hath been born; let us follow with the kings, even the Magi from the East, unto the place where the star doth direct their journey. (sessional hymn, Nativity Matins). Let us 'join the Magi', let us 'follow' and 'behold.’ The fast of the Nativity is our journey into a new and marvelous life in the Holy Trinity.
A journey is, by its nature, naturally ascetic. Unless my life is already humble, I cannot take all my possessions on a journey. I can never be too reliant on the plans I have made for my journey. In this case, a control lying beyond the self, i.e., God’s grace, must be admitted and accepted. This is the spirit to which the fast calls us.
A journey is, by its nature, also, an act of movement, of growth. What is old is left behind; newness is perceived and embraced; growth of understanding takes place. And even if the journey comes to a close in the same physical location from which it began, that place is no longer quite the same. This is the importance of the fast. The Nativity is a life-changing miracle for each one of us.
Make ready, O Bethlehem: let the manger be prepared, let the cave show its welcome. The Truth is come, the shadow is passed away; God hath appeared from a Virgin unto men formed as we are, and deifying that which He hath assumed. Wherefore, Adam is renewed with Eve, as they cry out: 'Thy good will hath appeared on earth to save our race’ (sticheron from the First Royal Hour).
We are renewed
Adam and Eve, all of humankind, are renewed and made alive in the Incarnation of God in Christ, who 'appeared on earth to save our kind.’ Fallen flesh, so long bound to death, so long yearning for growth and maturation into the fullness of life, is sewn into the garment of Christ and at last made fully alive. There is a pleasing old saying, with perhaps more than a touch of truth to it, that humankind drew its first full breath at the infant Christ's first cry.
We are called, then, to approach this great mystery as God's condescension into our own lives, personally and collectively. The Second Canon for the Nativity explains it clearly:
He layeth a path for us unto Heaven. The Nativity is not only about God's coming down to us, but about our rising up to Him, just as sinful humanity was lifted up into the person of Christ in the Incarnation itself.
We are called to arise, then, during the fast that is the journey to this Feast.
O Blessed One, that lookest down and seest all; keep us above sin, who ever sing Thy praises, steadfast and unmoved on the foundation of faith (from the Second Canon of the Nativity.) The faithful take up this call by abandoning those things which bind, rather than free, in order that a focus on God might become ever more real and central to our daily life. Meals are lessened and regimented, that a constant, lingering hunger may remind us of the great need we each have for spiritual food that goes beyond our daily bread. The number of Church services is gradually increased, that we might know whence comes that true food. Sweets and drink are set aside, that we might never feel content with the trivial and temporal joys of this world. Social engagements are reduced, that we might realize that all is not so well with us as we often take it to be. Anything which holds the slightest power over us, whether television or travel or recreation, is minimized or, better, cast wholly aside, that we might bring ourselves to be possessed and governed only by God.
Through this time of asceticism, the Church strips away common stumbling blocks into sin, in order to provide us with the self-perception that we lack in our typical indulgence, and to help us begin to grow the seeds of virtue. We must take up the task of our own purification, achieved only through God’s grace, that we might approach Him on Christmas Day as did the Magi and the shepherds in Bethlehem:
Come, O ye faithful, let us be lifted up with divine inspiration, and let us behold the divine condescension from on high that is made manifest to us in Bethlehem. And being cleansed in mind, by our way of life let us offer virtues in the stead of myrrh, faithfully preparing our entry into the Feast of the Nativity, storing up treasure in our souls and crying: Glory in the highest to God in Trinity, through Whom His good will is revealed to men, that as the Friend of man He may deliver Adam from the ancestral curse (from the Sixth Royal Hour).
The Mystery Brings Joy
Resurrection unto life is the ultimate gift of the Incarnation. Those in the Church journey toward the birth of Christ God during the Nativity fast by struggling up the mountain that is too steep to climb without God’s grace, that they might learn that unless a man understands that he is dead, he will never know the meaning of resurrection.
The fast is a holy and blessed tool that brings us closer to such selfawareness. It reveals to us who we are, perhaps more importantly, who we are not, and makes us more consciously aware of what we desperately need. Then and only then, with eyes opened, even if only partially, by the ascetic endeavor, we will truly know the life-giving light of the Nativity of Christ. We will hear with awe the proclamation of the hymn at Vespers, perceiving the mystery presented therein as having become truly an inward part of us.
Come, let us rejoice in the Lord as we declare this present mystery. The middle wall of partition is broken asunder; the flaming sword is turned back, the Cherubim withdraw from the Tree of Life, and I partake of the Paradise of Delight, whence I was cast out before through disobedience. For the Identical Likeness of the Father, the Express Image of His eternity, taketh the form of a servant, and without undergoing change He cometh forth from a Mother that knew not wedlock. For that which He was, He hath remained, even true God; and that which He was not, He hath taken upon Himself, becoming man out of love for man. Unto Him let us cry: O God, Who art born of a Virgin, have mercy on us (first sticheron from Vespers of the Nativity).
We will never fully comprehend this ineffable mystery of God become man; some knowledge is properly God's alone. But by His grace, through the ascetic effort, we will come at least to some understanding of the salvation of Christmas Day, of our own salvation. And with this realization comes joy— joy far greater than a mere entrance into the temple on Christmas Day could ever bring us. And having come through the forty days of the fast, with this joy in our hearts, we shall embrace the hymnographer’s words as our own.
On this day the Virgin cometh to the cave to give birth to God the Word ineffably, Who was before all the ages. Dance for joy O earth, on hearing the gladsome tidings; the angels and the shepherds now glorify Him Who is willing to be gazed on as a young Child Who before the ages is God (kontakion of the Forefeast).
Source 
