Tractates on the Gospel of John

² Whatever, then, you have heard stated in lowly manner concerning the Lord Jesus Christ, think of that economy by which He assumed flesh; but whatever you hear, or read, stated in the Gospel concerning Him that is sublime and high above all creatures, and divine, and equal and coeternal with the Father, be sure that this which you read appertains to the form of God, not to the form of the servant. For if you hold this rule, you who can understand it (inasmuch as you are not all able to understand it, but you are all bound to trust it)—if, I say, you hold this rule, as men walking in the light, you will fight against the calumnies of heretical darkness without fear.

For there have not been wanting those who, in reading the Gospel, followed only those testimonies that concern the humility of Christ, and have been deaf to those which have declared His divinity; deaf for this reason, that they may be full of evil words. There have likewise been some, who, giving heed only to those which speak of the excellency of the Lord, even though they have read of His mercy in becoming man for our sakes, have not believed the testimonies, but accounted them false and invented by men; contending that our Lord Jesus Christ was only God, not also man.

Some in this way, some in that: both in error. But the catholic faith, holding from both the truths which each holds and preaching the truth which each believes, has both understood that Christ is God and also believed Him to be man: for each is written and each is true. Should you assert that Christ is only God, you deny the medicine whereby you were healed: should you assert that Christ is only man, you deny the power whereby you were created. Hold therefore both. O faithful soul and catholic heart, hold both, believe both, faithfully confess both. Christ is both God and also man. How is Christ God? Equal with the Father, one with the Father. How is Christ man? Born of a virgin, taking upon Himself mortality from man, but not taking iniquity.