Everyone should read On the Incarnation by Athanasius. It is among the greatest and most influential works in Christian theology, and it is only around 60 pages in print. In his introduction to this Christian classic, C. S. Lewis debunks the myth that old books such as this are too hard for ordinary people to read. In fact, the greatest men are sometimes the easiest to understand, since they have mastered their material and are able to explain complicated concepts in simple terms.
I suggest reading this book every year (either at Christmas or Easter) and highly recommend the translation by John Behr in the Popular Patristics Series (SVS Press). While the full text of On the Incarnation is available for free online, Behr’s translation is easier to read, and it includes an excellent introduction to Athanasius and his writings. Also, print books are better than digital books for deep reading, in part because you can come to the text with a pen in hand. When reading deep texts, do not come with a bucket in hand, hoping to be filled up (passive reading); come with a shovel in hand, planning to dig for treasure (active reading). Your shovel is a pen!
The remainder of this article is a key except (around 900 words) from On the Incarnation, Chapters 8–9, in which Athanasius discusses why God became man. Because he pitied us when we were perishing because of sin, the Word (the Son of God) who was unable to die took on a human body like ours so that he would be able to die on behalf of all. Although Christ was one man, his death and resurrection had an effect on the whole human race because he united humanity with the power of divinity, put our shared nature to death on the cross, then raised it from the dead, “by the grace of the Resurrection, banishing death from them like straw from the fire” (On the Incarnation 8).
Much is lost by jumping into the text like this, but I pray that it will whet your appetite for the whole work. The text below is from The Complete Ante-Nicene & Nicene and Post-Nicene Church Fathers Collection, which is also available for free at ccel.org or newadvent.org, as well as on Kindle for $2.99. At a few places, I have added the text of Behr’s translation in brackets for clarification or where meaning may differ. I have also included additional paragraph breaks for readability. If you struggle, read slowly, read aloud, and reread as needed. If the meaning of a sentence eludes you, simply keep reading.
8. For this purpose, then, the incorporeal and incorruptible and immaterial Word of God [the Son of God, cf. John 1:1–3] comes to our realm, howbeit he was not far from us [Acts 17:27] before. For no part of Creation is left void of Him: He has filled all things everywhere, remaining present with His own Father. But He comes in condescension to show loving-kindness upon us, and to visit us.
2. And seeing the race of rational creatures in the way to perish [“seeing the rational race perishing,” Behr], and death reigning over them by corruption; seeing, too, that the threat against transgression gave a firm hold to the corruption which was upon us, and that it was monstrous that before the law was fulfilled it should fall through: seeing, once more, the unseemliness of what had come to pass: that the things whereof He Himself was Artificer [Creator] were passing away: seeing, further, the exceeding wickedness of men, and how little by little they had increased it to an intolerable pitch against themselves: and seeing, lastly, how all men were under penalty of death [“and seeing the liability of all human beings to death,” Behr]: He took pity on our race, and had mercy on our infirmity [weakness], and condescended to our corruption, and, unable to bear that death should have the mastery — lest the creature should perish, and His Father’s handiwork in men be spent for nought — He takes unto Himself a body, and that of no different sort from ours.
3. For He did not simply will to become embodied, or will merely to appear [“For he did not wish simply to be in a body,” Behr]. For if He willed merely to appear, He was able to effect His divine appearance by some other and higher means as well [“he could have made his divine manifestation through some other better means,” Behr]. But He takes a body of our kind, and not merely so, but from a spotless and stainless virgin, knowing not a man, a body clean and in very truth pure from intercourse of men. For being Himself mighty, and Artificer [Creator] of everything, He prepares the body in the Virgin as a temple unto Himself, and makes it His very own as an instrument, in it manifested, and in it dwelling.
4. And thus taking from our bodies one of like nature, because all were under penalty of the corruption of death [“since all were liable to the corruption of death,” Behr] He gave it over to death in the stead of all, and offered it to the Father — doing this, moreover, of His loving-kindness, to the end that, firstly, all being held to have died in Him [“with all dying in him,” Behr], the law involving the ruin of men [“concerning corruption in human beings,” Behr] might be undone (inasmuch as its power was fully spent in the Lord’s body, and had no longer holding-ground against men, his peers [“no longer having any ground against similar human beings,” Behr]), and that, secondly, whereas men had turned toward corruption, He might turn them again toward incorruption, and quicken them from death [“and give them life from death,” Behr] by the appropriation of His body [“by making the body his own,” Behr] and by the grace of the Resurrection, banishing death from them like straw from the fire.
9. For the Word, perceiving that no otherwise could the corruption of men be undone save by death as a necessary condition [“realizing that in no other way would the corruption of human beings be undone except, simply, by dying,” Behr], while it was impossible for the Word to suffer death, being immortal, and Son of the Father; to this end [“for this reason,” Behr] He takes to Himself a body capable of death, that it, by partaking of [“participating in,” Behr] the Word Who is above all, might be worthy to die in the stead of all [“sufficient for death on behalf of all,” Behr], and might, because of the Word which had come to dwell in it, remain incorruptible, and that thenceforth corruption might be stayed from all by the Grace of the Resurrection. Whence, by offering unto death the body He Himself had taken, as an offering and sacrifice free from any stain, straightway He put away death from all His peers by the offering of an equivalent [“he immediately abolished death from all like him, by the offering of a like,” Behr].
2. For being over all, the Word of God naturally by offering His own temple and corporeal instrument for the life of all [“bodily instrument as a substitute for all,” Behr] satisfied the debt by His death [“fulfilled in death that which was required,” Behr]. And thus He, the incorruptible Son of God, being conjoined with all by a like nature, naturally clothed all with incorruption, by the promise of the resurrection. For the actual corruption in death has no longer holding-ground against men, by reason of the Word, which by His one body has come to dwell among them [“the very corruption of death no longer holds ground against human beings because of the indwelling Word, in them through the one body,” Behr].
3. And like as when a great king has entered into some large city and taken up his abode in one of the houses there, such city is at all events held worthy of high honour, nor does any enemy or bandit any longer descend upon it and subject it; but, on the contrary, it is thought entitled to all care, because of the king’s having taken up his residence in a single house there: so, too, has it been with the Monarch [King] of all.
4. For now that He has come to our realm, and taken up his abode in one body among His peers [“dwelling in a body like the others,” Behr], henceforth the whole conspiracy of the enemy against mankind is checked [“every design of the enemy against human beings has henceforth ceased,” Behr], and the corruption of death which before was prevailing against them is done away. For the race of men had gone to ruin, had not the Lord and Saviour of all, the Son of God, come among us to meet the end of death [“for the completion of death,” Behr].