Now if these things are so, out of these things are rebutted those which they subsequently object to us. For what catholic would say that which they charge us with saying, “that the Holy Spirit was not the assister of virtue in the old testament,” unless when we so understand “the old testament” in the manner in which the apostle spoke of it as “gendering from Mount Sinai into bondage”? But because in it was prefigured the new testament, the men of God who at that time understood this according to the ordering of the times, were indeed the stewards and bearers of the old testament, but are shown to be the heirs of the new. Shall we deny that he belongs to the new testament who says, “Create in me a clean heart, O God; and renew a right spirit within me”? or he who says, “He hath set my feet upon a rock, and directed my goings; and he hath put a new song in my mouth, even a hymn to our God”? or that father of the faithful before the old testament which is from Mount Sinai, of whom the apostle says, “Brethren, I speak after the manner of men; yet even a man’s testament, when it is confirmed, no man disannulleth or addeth thereto. To Abraham and to his seed were the promises made. He saith not, And to seeds, as of many, but as of one; and to thy seed, which is Christ. And this I say,” said he, “that the testament confirmed by God, the law which was made four hundred and thirty years after, does not weaken, so as to make the promise of none effect. For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise.”
Reproduced in full. Translation: Nicene and Post-Nicene Fathers, series 1, vol. 5 (Schaff, 1887), public domain (Public domain).