Exod 17:12

“For it was not because Moses so prayed that the people were stronger, but because, while one who bore the name of Jesus (Joshua) was in the forefront of the battle, he himself made the sign of the cross. For who of you knows not that the prayer of one who accompanies it with lamentation and tears, with the body prostrate, or with bended knees, propitiates God most of all? But in such a manner neither he nor any other one, while sitting on a stone, prayed. Nor even the stone symbolized Christ, as I have shown.”

“But, to come now to Moses, why, I wonder, did he merely at the time when Joshua was battling against Amalek, pray sitting with hands expanded, when, in circumstances so critical, he ought rather, surely, to have commended his prayer by knees bent, and hands beating his breast, and a face prostrate on the ground; except it was that there, where the name of the Lord Jesus was the theme of speech—destined as he was to enter the lists one day singly against the devil—the figure of the cross was also necessary, [that figure] through which Jesus was to win the victory?”

“See how the type was given through Moses but the truth came through Jesus Christ. And again, on Mt. Sinai, when the Amalekites were waging war on the Hebrews, the hands of Moses were propped up, held by Aaron and Hur standing on either side. But Christ, when he came, himself held his hands extended on the cross by his own power. Do you see how the type "was given" and "the truth came"?”

“When Moses' hands were lifted up Amalek was conquered; when they came down a little he grew strong. The sailyards of ships and the ends of the sailyards move about in the form of our cross. The very birds, too, when they are borne to the heights and fly through the air, imitate the cross with their wings outstretched. Trophies themselves are crosses, and so are adorned victories of triumphs. These we ought to have not only on our foreheads but also on our souls so that, thus armed, we may trample upon the adder and the serpent, in Christ Jesus, to whom be glory forever.”

“When Moses sat on the stone, it prefigured the law resting on the church. But this law had heavy hands, because it did not deal mercifully with those who were sinners but treated them with extreme harshness. "Aaron" means "mountain of strength," and "Hur" means "fire." Who is meant by "mountain of strength"? Our Redeemer, of whom the prophet said, "It shall come to pass in the latter days that the mountain of the house of the Lord shall be established as the highest of the mountains." And who is prefigured by "fire" but the Holy Spirit, of whom our Redeemer said, "I have come to cast fire upon the earth"? Aaron and Hur support the heavy hands of Moses and make them lighter by their support. Similarly the "Mediator between God and men," coming with the fire of the Holy Spirit, revealed that the heavy commandments of the law, which cannot be borne when taken literally, become more tolerable for us when they are understood spiritually. It is as if he made the hands of Moses light when he changed the weight of the law's commandments into the strength that comes from confession.”