Christology — who exactly is Jesus?

Jesus put the question himself, and he put it to his closest friends rather than to a crowd: "But who do you say that I am?" (Matthew 16:15).

Everything turns on the answer. If he is who he claimed, no other question is more urgent. If he is not, Christianity is a two-thousand-year mistake built on a misunderstanding of a Galilean carpenter.

Fully God

He is called God directly. "In the beginning was the Word, and the Word was with God, and the Word was God" (John 1:1). Thomas, seeing the risen Christ, says "My Lord and my God!" (John 20:28) — and Jesus commends him rather than correcting him, which he would have been obliged to do if it were blasphemy. Paul writes of "our great God and Saviour Jesus Christ" (Titus 2:13). "In him the whole fullness of deity dwells bodily" (Colossians 2:9).

He does what only God does. He forgives sins committed against other people — and the scribes react correctly: "who can forgive sins but God alone?" (Mark 2:7). He commands nature. He raises the dead by his own authority. He will judge the world.

He takes the divine name. "Truly, truly, I say to you, before Abraham was, I am" (John 8:58) — bad grammar deliberately, because he is quoting Exodus 3:14. The response is immediate: they pick up stones. There is no misunderstanding to clear up.

He accepts worship. Angels refuse it (Revelation 22:8-9). Peter refuses it (Acts 10:25-26). Paul and Barnabas tear their clothes in horror when offered it (Acts 14:14-15). Jesus receives it repeatedly and never once deflects it.

Fully man

The opposite error is equally fatal, and it came first historically. Docetism — from dokeō, to seem — held that Jesus only appeared to be human, a spirit wearing a body, because the divine could not touch matter.

John writes against it in his own lifetime: "every spirit that confesses that Jesus Christ has come in the flesh is from God" (1 John 4:2). He opens his letter insisting on physical evidence: what we have heard, seen with our eyes, touched with our hands (1 John 1:1).

The Gospels are relentlessly physical. He was born of a woman (Galatians 4:4). He grew — "increased in wisdom and in stature" (Luke 2:52), meaning there were things he did not yet know. He got tired (John 4:6) and slept through a storm (Mark 4:38). He was hungry (Matthew 4:2) and thirsty (John 19:28). He wept (John 11:35). He was "tempted as we are, yet without sin" (Hebrews 4:15). He bled, died, and afterwards ate fish (Luke 24:42-43) to prove he was not a ghost.

One person, two natures

The formula the church arrived at, at Chalcedon in AD 451, is precise because every imprecision had already been tried and had broken something:

One and the same Christ, Son, Lord, Only-begotten, made known in two natures, without confusion, without change, without division, without separation.

Four negatives, each ruling out a specific error:

• Without confusion / without change — the natures are not blended into a third thing. Against Eutychianism.
• Without division / without separation — he is not two persons in partnership. Against Nestorianism.

The technical name is the hypostatic union: two complete natures, divine and human, united in one person. Not fifty per cent each. One hundred per cent of both.

This is why some sentences about Jesus are true of one nature and not the other. He is omniscient in his deity and says he does not know the day or hour in his humanity (Mark 13:32). He sleeps in the boat and stills the storm from the same boat, minutes apart.

The heresies, and what each one costs

Every early error denied one half of the formula, and every one of them breaks salvation. This is why the church fought about words with such intensity — they were not arguing about vocabulary.

• Arianism — the Son is the highest created being. Cost: a creature cannot save creatures; and worshipping him becomes idolatry. (This is essentially the Jehovah's Witness position today.)
• Docetism — his humanity was an appearance. Cost: he did not really die, so nothing was really paid.
• Nestorianism — two persons loosely joined. Cost: which one died? A human person dying is just another execution.
• Eutychianism — the natures blend into a hybrid. Cost: he is then neither truly God nor truly man, and represents neither party.
• Adoptionism — a man who was promoted to divine status. Cost: the incarnation never happens; God never comes.

Why both natures are load-bearing

Anselm framed it in the eleventh century and it has not been improved on. Salvation required someone who ought to pay — a human being, since the debt is humanity's — and someone who could pay — God, since no creature has the resources.

Only one person in history has ever been both.

His humanity means he can substitute for us. "Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death" (Hebrews 2:14).

His deity means the substitution is sufficient. One life for many, because the life is of infinite worth.

And both mean he understands. "We do not have a high priest who is unable to sympathise with our weaknesses, but one who in every respect has been tempted as we are, yet without sin" (Hebrews 4:15).

That last one is not a footnote. Whatever you are carrying, you are not explaining it to someone who has only read about it.

He became what we are that he might make us what he is.— Athanasius, On the Incarnation