On the Incarnation is the classic Christian answer to a simple, enormous question: why did God become man? It was written around the year 318 by Athanasius, then a young deacon of Alexandria, who would spend the rest of his life defending the full deity of Christ against the whole weight of the empire. It is short, clear, and astonishingly confident, and it has never been bettered as an introduction to why Christmas and Good Friday had to happen. C. S. Lewis, who wrote a famous preface to a modern translation, said it was a masterpiece that read like the work of a mind that had thought its way clean through the subject.
This guide explains who wrote it, what it argues step by step, its most famous sentence, and how to read a book seventeen centuries old without getting lost. The full text is free in the Ochorus library.
Who wrote it, and when
Athanasius (roughly 296–373) was born in Alexandria, the great intellectual city of the Christian east, and grew up in the church there during the last persecutions. He wrote On the Incarnation as a young man, probably before the great controversy that would define his life had fully broken out. Within a few years the priest Arius would begin teaching that the Son was a created being, less than fully God, and Athanasius would spend the next half-century — as bishop of Alexandria, exiled five times by four emperors — insisting that if Jesus is not fully God, we are not saved. This early book already contains the conviction that would cost him so much: that only God can save, and that therefore the Saviour must be God.
It is worth reading, then, not as dry theology but as the first statement of a case Athanasius would defend at the risk of his life. The confidence in it is the confidence of a man who had thought the matter through to the bottom.
The problem: death and corruption
Athanasius begins with creation. God made the world out of nothing, and made human beings in his own image, meant to know him and live. But humanity turned from God to nothing, and in turning from the source of life fell back toward the nothing it came from — into corruption and death. Romans 5:12 is the story: by one man sin entered the world, and death by sin. This left God, as Athanasius frames it, with a genuine dilemma. His justice had said that sin would bring death; that word could not simply be broken. But his goodness could not let the creatures made in his image be swallowed by corruption. Repentance alone could not fix it, because repentance does not reverse corruption; it does not undo death or restore what sin has ruined.
So the problem required someone who could do two things at once: pay the debt of death that all owed, and, being himself the Life, defeat death from the inside. No mere human could do it, because humans were the ones in debt. Only the Word of God, through whom everything was made, could take a body, die the death owed by all, and by his own indestructible life burst death open. John 1:14 is the hinge of the whole argument: the Word was made flesh, and dwelt among us.
The answer: the Word takes a body
The centre of the book is the reasonableness of the Incarnation. The Word who was always present everywhere, upholding all things, took to himself a real human body — not ceasing to fill the universe, but now also present in a particular man. He did this, Athanasius argues, for interlocking reasons. To pay death’s claim: an incorruptible body, offered in death on behalf of all, satisfied the sentence and ended it for all who are joined to him. To restore the image: humanity had defaced the portrait of God in itself, and the only way to repaint a ruined portrait is for the original to sit for it again, so the Image himself came in person. And to teach us the Father: because people had sunk into worshipping creation and could no longer read God in the world, the Word came in a body they could see, to draw their sense-bound attention back to God.
Then comes the sentence the book is remembered for, the boldest expression of what salvation finally means:
He was made man that we might be made God; and He manifested Himself by a body that we might receive the idea of the unseen Father.
Athanasius, On the Incarnation
The phrase startles modern readers, but Athanasius does not mean that we become gods in our own right. He means what 2 Peter 1:4 means by becoming partakers of the divine nature: that in Christ, human beings are lifted into the life of God, made incorruptible, adopted, and brought to share what is his by grace. God came down to where we were so that we might be raised to where he is.
The victory over death
The later chapters turn to the resurrection, and here Athanasius is at his most exhilarating. The proof that death is defeated, he says, is not merely an argument but a fact you can watch: Christians have stopped being afraid to die. Where death once ruled everyone by fear, now ordinary believers — including women and children, he notes — tread it underfoot and even choose martyrdom rather than deny Christ. Hebrews 2:14–15 is exactly his point: Christ shared our flesh so that through death he might destroy the one who had the power of death, and free those who through fear of death were all their lifetime in bondage. Athanasius puts it plainly:
Death is no longer terrible; for all who believe in Christ tread him under as nought.
Athanasius, On the Incarnation
He even asks why the death had to be public, on a cross, and not quiet and private — and answers that a hidden death could not have proved a resurrection, whereas a death witnessed by enemies, followed by a risen life witnessed by friends, could. 1 Corinthians 15:3–4, that Christ died, was buried, and rose again, is being defended here as history, not myth.
Why it mattered enough to fight for
It is worth seeing why this book’s argument was worth a lifetime of exile. Athanasius’s whole case rests on the Saviour being truly God. If the Word who took a body were merely a very exalted creature, as Arius taught, then the death on the cross would be the death of a creature, unable to pay the debt of all; the life poured into believers would be a creature’s life, unable to make them incorruptible; and the union with God the book promises would be impossible, because a creature cannot bridge the gap between God and the world. Everything Athanasius says about salvation collapses the moment Christ is less than fully God. That is why he would not yield an inch, through five exiles and the hostility of emperors. Titus 2:13 was at stake — the appearing of the glory of our great God and Saviour Jesus Christ — and with it, he believed, salvation itself.
The book is therefore not a museum piece but the foundation under every later statement of the faith. When the Council of Nicaea confessed the Son as of one being with the Father, it was defending exactly what this early book had already seen: that only God can save, so the Saviour must be God. Read it and you are reading the logic beneath the creed that most of the world’s Christians still recite. Hebrews 1:3 states the conviction in a line — the Son is the brightness of God’s glory and the express image of his person — and Athanasius spent his life making sure the church never let go of it.
How to read it today
Read Lewis’s preface first if your edition has it. It is a small classic in its own right, and its argument for reading old books — that every age is blind in its own way and old books correct us — is worth the price on its own.
Do not get stuck on the fourth-century frame. Athanasius argues against pagan idolatry and Jewish objections that are not live for most modern readers. Let those sections go by; the spine of the book — the problem of death, the reason for the Incarnation, the victory of the resurrection — is timeless.
Read the famous sentence in context. “That we might be made God” has a precise meaning; read the surrounding paragraphs and 2 Peter 1:4, and it becomes glorious rather than strange.
Read it at Christmas or Easter. It is the best possible companion to either. It explains why the manger and the empty tomb belong to the same argument, and why neither makes sense without the God who chose to enter his own creation.
Read Augustine’s Confessions next. Athanasius gives you the doctrine of what God did; Augustine, a generation later, shows you that doctrine reaching into one restless life. Together they are the two indispensable voices of the early church.
Athanasius wrote to prove one thing: that God so loved the world, as John 3:16 says, that he did not stay outside it. He came in, took a body, met our death, and broke it, so that we might share his life. Seventeen centuries later it is still the clearest short answer to the question the whole faith turns on — why God became man.