This is a homily I preached at our school chapel last Advent. The text is one I chose, though I don't really remember what led me to it.
‘Afterward thou shalt be called “the city of righteousness, the faithful city”. Zion shall be redeemed by justice, and her converts with righteousness.’
In the name of the Father and of the Son and of the Holy Spirit. Amen.
It is fitting as we begin the period of Advent, patiently, or sometimes impatiently, expecting the adventus or coming of our Lord Jesus Christ, that we look back to the prophecies of the Old Testament that foretell the mighty works He came and will come again to perform. Today’s reading from the prophet may seem to strike a dark note at first, for it concerns the unfaithfulness of the holy city of Zion--Jerusalem. The Prophet Isaiah says the city has become a harlot or adulteress, that she is greedy and without charity or justice. It’s easy to read this and think smugly to ourselves, ‘Wow, those people were bad.’ But we miss the point entirely if we read this prophecy merely as a history of some place in the Middle East thousands of years ago.
For ‘the city’ is us, human beings. This is the Lord’s way of giving us a picture, because we all have some idea of what a city is like, though most of our modern cities are rather poor things. But it is a deeply significant picture. It means human beings are not just individual people, totally separate from each other, but people made for each other. St Chrysostom says, ‘Do you see how many bonds of love God has created? He’s done so as forces of nature lodged in us to be pledges of our peace with one another. We are of the same substance….God made us to need one another...’  Even the great hermit, St Anthony, who spent 30 years in prayer with God alone, says ironically, ‘Our life and our death is with our neighbour’,  and because of this teaching, as St Athanasius writes, even ‘the desert was made a city’.  We must begin by realising that human beings are all neighbours, we are a family. In a famous book based on this image of ‘the city’, St Augustine writes:
‘And human nature has nothing more appropriate, either for the prevention of discord, or for the healing of it, where it exists, than the remembrance of that first parent of us all, whom God was pleased to create alone, that all men might be derived from one, and that they might thus be admonished to preserve unity among their whole multitude.’ 
Thus our first mother Eve was taken out of the side of our father Adam, and the two were given to each other to help one another. But the sin of the Fall has split this familial unity that St Augustine speaks of, and we have become the broken family that St Augustine calls ‘the city of man’. For ‘the founder of the earthly city was a fratricide’--Cain, the murderer of ‘his own brother, a citizen of the eternal city, and a sojourner on earth’. 
And thus, as the Prophet says, the city of man has become full of murderers now (1:21)--for Christ says we are all guilty of murder whenever we become angry with our brother or insult him.
The Prophet says the city’s ‘silver is become dross’ (1:22)--which as Matthew Henry says means that moral corruption and injustice in the powerful among society is worse than economic decline. 
The Prophet says the city’s ‘wine is mixed with water’ (1:22)--meaning the sweetness and fellowship of human life has become flavourless due to our sin.
The Prophet says that the princes--our leaders--have become rebellious against God--the companions of thieves--defrauding the poor--greedy for profits and bribes--allowing the oppression and exploitation of the powerless--calling the orphans and the widows and the homeless lazy, dishonest, thieves, and drunkards, when it is really the powerful who are all these things. (1:23)
It is this city of which Socrates prophetically warned his pupil Alicibiades, ‘I know the city, and I fear that it shall get the better of both of us’ --of the pupil, because it would seduce him to a life of sin, and of the teacher, because it would put him to death unjustly.
So God says He will ‘avenge’ Him ‘of His enemies’ (1:24). He will say: ‘Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels: for I was an hungred, and ye gave me no meat: I was thirsty, and ye gave me no drink: I was a stranger, and ye took me not in: naked, and ye clothed me not: sick, and in prison, and ye visited me not.’ (Matt. 25:41-3)
This is the fate of what St Augustine calls ‘the city of man’, and it is depicted well in Dante’s Inferno, where Dante beholds ‘the city they call Dis, / with its great hosts, with its grave citizens’. 
But thanks be to God, there is another City, which St Augustine calls ‘the City of God’--because as St John says, when he sees it ‘coming down from God out of heaven, prepared as a bride adorned for her husband’ (‘in the purity and virtue of the saints’), it ‘has the glory of God in it’ lightening it more brilliantly than even the sun could do (Rev. 21:2, 11, 23). It is a city of the converts, of the repentant, restored to beauty and order--and love--by the Lord, and thus as St Andrew of Crete writes, ‘This city, which has Christ as its cornerstone, is composed of the saints concerning whom it is written: They shall be as the stones of a crown, lifted up as an ensign upon His land (Zech. 9:16)’ .
It is a city marked by justice and charity between all, where ‘the love that moves the sun and the stars’ binds everyone together forever. In an essay called ‘The Redeemed City’, the eccentric Anglican man of letters, Charles Williams writes:
In the last paragraph of the Apostles’ Creed the City is defined. ‘I believe in the Holy Ghost’ is its first clause and primal condition….Simultaneously all its citizens derive from all. ‘The Holy Catholic Church’ is its name here, allowing for all proper implications of whatever kind....But the other four clauses are, as it were, the four walls of the description [of St John] in the Apocalypse; or, if the metaphor divides them too much, say they are the four qualities of that life: ‘the Communion of Saints, the Forgiveness of Sins, the Resurrection of the Body, and the Life everlasting’. They are the qualities of the renewed perfection of union--interchange, interchange redeeming even the denial of itself...The almost incredible nature of things is that there is no fact which is not His glory. This is the great inclusion which makes the City. If, to use terms of space, we ascend towards it, it is still that which descends out of heaven, and is the cause and course of our ascent. The language of it is in the great interchange of fiery tongues by which the Spirit manifested at the beginning. 
But we mustn’t forget that all of this does not simply happen magically. As the Lord says through His prophet, ‘I will turn my hand against you and will smelt away your dross as with lye and remove all your alloy’ (Is 1:25). We must be purged of our sins and passions, and begin to practice the commandments of Christ if we are to become the City of God. So as we embark upon this journey that will lead us to the little city of Bethlehem, and to worship the great King whose birth is proclaimed with the words ‘Glory to God in the highest, and on earth peace towards men of good will’, let us remember to do our part in symphony with His grace to live with justice, to show love towards all in our earthly city here and now, and to comfort the outcasts and afflicted in the streets, so that we may one day behold the heavenly City, where ‘God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away’ (Rev 21:4).
For the city of the great King is well planted on the mountains of Sion, with the joy of the whole earth, on the sides of the north. God is known in her palaces, when he undertakes to help her. (Ps 47:2-3 LXX)
In the name of the Father and of the Son and of the Holy Spirit. Amen.
 Homily 34.6; St John Chrysostom, The Love Chapter: The Meaning of First Corinthians 13 (Brewster, MA: Paraclete, 2010), pp. 78-9.
 Apopophegmata Patrum, Anthony 9; Benedicta Ward, SLG, tr., The Sayings of the Desert Fathers: The Alphabetical Collection, rev. ed. (Kalamazoo, MI: Cistercian, 1984), p. 3.
 Vita Antonii 14; St Athanasius, The Life of Antony & the Letter to Marcellinus, tr. Robert C. Gregg (Mahwah, NJ: Paulist, 1980), pp. 42-3.
 De Civitate Dei 12.27; St Augustine, The City of God, tr. Marcus Dods (NY: Modern Library, 1950), p. 410.
 De Civitate Dei 15.5; St Augustine, p. 482.
 Matthew Henry, Commentary on the Whole Bible: New One Volume Edition, ed. Leslie F. Church (Grand Rapids, MI: Zondervan, 1966), p. 828.
 Alcibiades 135e; Plato, ‘Alcibiades’, tr. D.S. Hutchinson, The Complete Works, ed. John M. Cooper & D.S. Hutchinson (Indianapolis: Hackett, 1997), p.
 Inferno 8.68-9; Dante Alighieri, Inferno, tr. Anthony Esolen (NY: Modern Library, 2003), p. 81.
 In Archbishop Averky, The Apocalypse in the Teachings of Ancient Christianity, tr. & ed. Hieromonk Seraphim (Rose) (Platina, CA: St Herman of Alaska Brotherhood, 1998), p. 268.
 Charles Williams, The Image of the City & Other Essays, ed. Anne Ridler (London: Oxford U, 1970), p. 110.