Genesis 22:13

This “wood,” again, Isaac the son of Abraham personally carried for his own sacrifice, when God had enjoined that he should be made a victim to Himself. But, because these had been mysteries which were being kept for perfect fulfilment in the times of Christ, Isaac, on the one hand, with his “wood,” was reserved, the ram being of fered which was caught by the horns in the bramble; Christ, on the other hand, in His times, carried His “wood” on His own shoulders, adhering to the horns of the cross, with a thorny crown encircling His head. …

2. All instruction is either about things or about signs; but things are learnt by means of signs. I now use the word “thing” in a strict sense, to signify that which is never employed as a sign of anything else: for example, wood, stone, cattle, and other things of that kind. Not, however, the wood which we read Moses cast into the bitter waters to make them sweet, nor the stone which Jacob used as a pillow, nor the ram which Abraham offered up instead of his son; for these, though they are things, are also signs of other things. There are signs of another kind, those which are never employed except as signs: for example, words. No one uses words except as signs of something else; and hence may be understood what I call signs: those things, to wit, which are used to indicate something else. Accordingly, every sign is also a thing; for what is not a thing is nothing at all. …

79. It is better to make no vow than to vow what God does not wish to be paid to Him to Whom the promise was made. In the case of Isaac we have an example, for the Lord appointed a ram to be offered up instead of him. Therefore it is not always every promise that is to be fulfilled. Nay, the Lord Himself often alters His determination, as the Scriptures point out. For in the book called Numbers He had declared that He would punish the people with death and destroy them, but afterwards, when besought by Moses, He was reconciled again to them. And again, He said to Moses and Aaron: “Separate yourselves from among this congregation that I may consume them in a moment.” And when they separated from the assembly the earth suddenly clave asunder and opened her mouth and swallowed up Dathan and Abiram.

98. The father offered indeed his son, but God is appeased not by blood but by dutiful obedience. He showed the ram in the thicket in the stead of the lad, that He might restore the son to his father, and yet the victim not fail the priest. And so Abraham was not stained with his son’s blood, nor was God deprived of the sacrifice. The prophet spoke, and neither yielded to boastfulness nor continued obstinate, but took the ram in exchange for the lad. And by this is shown the more how piously he offered him whom he now so gladly received back. And thou, if thou offer thy gift to God, dost not lose it. But we are tenacious of our own; God gave His only Son for us, we refuse ours. …