John of Damascus: Exposition of the Orthodox Faith 70Concerning the Passion of our Lord's body, and the Impassibility of His divinity.

The Word of God then itself endured all in the flesh, while His divine nature which alone was passionless remained void of passion. For since the one Christ, Who is a compound of divinity and humanity, and exists in divinity and humanity, truly suffered, that part which is capable of passion suffered as it was natural it should, but that part which was void of passion did not share in the suffering. For the soul, indeed, since it is capable of passion shares in the pain and suffering of a bodily cut, though it is not cut itself but only the body: but the divine part which is void of passion does not share in the suffering of the body.

Observe, further, that we say that God suffered in the flesh, but never that His divinity suffered in the flesh, or that God suffered through the flesh. For if, when the sun is shining upon a tree, the axe should cleave the tree, and, nevertheless, the sun remains uncleft and void of passion, much more will the passionless divinity of the Word, united in subsistence to the flesh, remain void of passion when the body undergoes passion. And should any one pour water over flaming steel, it is that which naturally suffers by the water, I mean, the fire, that is quenched, but the steel remains untouched (for it is not the nature of steel to be destroyed by water): much more, then, when the flesh suffered did His only passionless divinity escape all passion although abiding inseparable from it. For one must not take the examples too absolutely and strictly: indeed, in the examples, one must consider both what is like and what is unlike, otherwise it would not be an example. For, if they were like in all respects they would be identities, and not examples, and all the more so in dealing with divine matters. For one cannot find an example that is like in all respects whether we are dealing with theology or the dispensation.