23 So the Man Jesus Christ, Only-begotten God, as flesh and as Word at the same time Son of Man and Son of God, without ceasing to be Himself, that is, God, took true humanity after the likeness of our humanity. But when, in this humanity, He was struck with blows, or smitten with wounds, or bound with ropes, or lifted on high, He felt the force of suffering, but without its pain. Thus a dart passing through water, or piercing a flame, or wounding the air, inflicts all that it is its nature to do: it passes through, it pierces, it wounds; but all this is without effect on the thing it strikes; since it is against the order of nature to make a hole in water, or pierce flame, or wound the air, though it is the nature of a dart to make holes, to pierce and to wound.
So our Lord Jesus Christ suffered blows, hanging, crucifixion and death: but the suffering which attacked the body of the Lord, without ceasing to be suffering, had not the natural effect of suffering. It exercised its function of punishment with all its violence; but the body of Christ by its virtue suffered the violence of the punishment, without its consciousness. True, the body of the Lord would have been capable of feeling pain like our natures, if our bodies possessed the power of treading on the waters, and walking over the waves without weighing them down by our tread or forcing them apart by the pressure of our steps, if we could pass through solid substances, and the barred doors were no obstacle to us.
But, as only the body of our Lord could be borne up by the power of His soul in the waters, could walk upon the waves, and pass through walls, how can we judge of the flesh conceived of the Holy Ghost on the analogy of a human body? That flesh, that is, that Bread, is from Heaven; that humanity is from God. He had a body to suffer, and He suffered: but He had not a nature which could feel pain. For His body possessed a unique nature of its own; it was transformed into heavenly glory on the Mount, it put fevers to flight by its touch, it gave new eyesight by its spittle.
Source: On the Trinity (New Advent)