On the Holy Spirit: The aforesaid unity is proved hereby, that as the Father is said to be grieved and tempted, so too the Son. The Son was also tempted in the wilderness, where a figure of the cross was set up in the brazen serpent: but the Apostle says that the Spirit also was there tempted. St. Ambrose infers from this that the Israelites were guided into the promised land by the same Spirit, and that His will and power are one with those of the Father and the Son

48. And we may behold this unity also in other passages of the Scriptures. For whereas Ezekiel says to the people of the Jews: “And thou hast grieved Me in all these things, saith the Lord;” Paul says to the new people in his Epistle: “Grieve not the Holy Spirit of God, in Whom ye were sealed.” Again, whereas Isaiah says of the Jews themselves: “But they believed not, but grieved the Holy Spirit;” David says of God: “They grieved the Most High in the desert, and tempted God in their hearts.”

49. Understand also that whereas Scripture in other places says that the Spirit was tempted, and that God was tempted, it says also that Christ was tempted; for you have the Apostle saying to the Corinthians: “Neither let us tempt Christ, as some of them tempted, and perished by serpents.” Just was the punishment that the adversaries should feel the venom, who had not venerated the Maker.

50. And well did the Lord ordain that by the lifting up of the brazen serpent the wounds of those who were bitten should be healed; for the brazen serpent is a type of the Cross; for although in His flesh Christ was lifted up, yet in Him was the Apostle crucified to the world and the world to him; for he says: “The world hath been crucified unto me, and I unto the world.” “So the world was crucified in its allurements, and therefore not a real but a brazen serpent was hanged; because the Lord took on Him the likeness of a sinner, in the truth, indeed, of His Body, but without the truth of sin, that imitating a serpent through the deceitful appearance of human weakness, having laid aside the slough of the flesh, He might destroy the cunning of the true serpent. And therefore in the Cross of the Lord, which came to man’s help in avenging temptation, I, who accept the medicine of the Trinity, recognize in the wicked the offence against the Trinity.

51. Therefore when you find in the book of Moses, that the Lord being tempted sent serpents on the people of the Jews, it is necessary that you either confess the Unity of the Father, Son, and Holy Spirit in the Divine Majesty, or certainly when the writing of the Apostle says that the Spirit was tempted, it undoubtedly pointed out the Spirit by the name of Lord. But the Apostle writing to the Hebrews says that the Spirit was tempted, for you find this: “Wherefore the Holy Ghost saith this: Today if ye shall hear His voice, harden not your hearts, like as in the provocation in the day of temptation in the wilderness, where your fathers tempted Me, proved Me, and saw My works. Forty years was I near to this generation and said: They do alway err in their heart; but they did not know My ways, as I sware in My wrath, If they shall enter into My rest.”

52. Therefore, according to the Apostle, the Spirit was tempted. If He was tempted, He also certainly was guiding the people of the Jews into the land of promise, as it is written: “For He led them through the deep, as a horse through the wilderness, and they laboured not, and like the cattle through the plain. The Spirit came down from the Lord and guided them.” And He certainly ministered to them the calm rain of heavenly food, He with fertile shower made fruitful that daily harvest which earth had not brought forth, and husbandman had not sown.

53. Now let us look at these points one by one. God had promised rest to the Jews; the Spirit calls that rest His. God the Father relates that He was tempted by the unbelieving, and the Spirit says that He was tempted by the same, for the temptation is one wherewith the one Godhead of the Trinity was tempted by the unbelieving. God condemns the people of the Jews, so that they cannot attain to the land flowing with milk and honey, that is, to the rest of the resurrection; and the Spirit condemns them by the same decree: “If they shall enter into My rest.” It is, then, the decree of one Will, the excellency of one Power.