It is well known that when a piece of iron is placed in the fire until it glows white like the white flame itself, its activity becomes a single activity; it no longer has two distinct operations—one attributable to the iron and the other to the fire. Rather, it now contains the strength of the iron and the strength of the fire, indeed a third potency that is neither purely the power of iron nor purely the power of fire, for it is no longer simple iron nor simple fire.

Likewise, when water is mixed with milk and wine, the resultant compound is one thing whose action is one action, though within it there is something that is neither pure water nor pure milk. No rational person would say that it now possesses two separate actions, one arising from its being pure milk and another from its being pure water. Hence their doctrine of “union” necessitates that the divinity be transformed into the humanity and that the action of the unified entity become a single action.

If, on the other hand, the divine nature has not united with him, then there are two persons, two essences, two natures, and two wills—and that is not the faith of the Christians—while the indwelling of the Lord, Exalted is He, in a human being is impossible, as has been set out elsewhere.

The same objection applies when they compare it to the soul’s relationship with the body: the soul’s attributes change when it separates from the body, and the body’s attributes likewise change when the spirit leaves it.

And the human being into whom the spirit has been breathed, so that he is a body endowed with a spirit, is—