It is part of the goodness of God, that He, who has no beginning and no ending, the Eternal Trinity, should take such care to give us a year which begins and ends, and then begins all over again. In our human and finite state we need fresh starts, and this is one of them. From the peaks of Pascha, Ascension, Pentecost, and Transfiguration, we move back to beginnings, the Nativity of the Mother of God, and then in December of the Son of God Himself. We start this wonderful cycle all over again. But the Holy Spirit, as we trust Him, will renew this new year to us, and give us a whole new understanding of it.
"Behold I will do a new thing", God says through the prophet Isaiah (43:19). The new wine will come to us in new wineskins.
The God who has put eternity in our hearts, knows our human frailty. He knows that marriages need their anniversaries, and all of us, especially children, need their birthdays from year to year. We in the Orthodox Church also hold a special place for the anniversaries of those who have died in Christ. We recall every year the glorious deaths of the saints. But the whole of this is held in a solid framework - the Orthodox Calendar. Through the God inspired wisdom of our fathers and mothers, we have a beautifully constructed lectionary, which flows through the year, like the streams of an effortless river, blessing whatever they touch.
It is significant that the last great feast of the old year is that of the Dormition of Mary, the Mother of God. Her human passing was to heaven's glory. And the first great feast of the new year is her Nativity. It is not that Mary is more important that Christ, around which most of the Calendar revolves. Mary is not God. She did not exist from eternity. But she is honoured in this way because she is our supreme example. She lived a life of complete obedience to God.