An excerpt from his Against Heresies (Book 4)
For this reason John in the book of Revelation says: His voice was as the voice of many waters. The Spirit of God is indeed a multitude of waters, for the Father is rich and great. As the Word passed among all these people he provided help in generous measure for those who were obedient to him, by drawing up a law that was suitable and fitting for every circumstance.
He established a law for the people governing the construction of the tabernacle and the building of the temple, the choice of Levites, the sacrifices, the offerings, the rites of purification and the rest of what belonged to worship.
He himself needs none of these things. He is always filled with all that is good. Even before Moses existed he had within himself every fragrance of all that is pleasing. Yet he sought to teach his people, always ready though they were to return to their idols. Through many acts of indulgence he tried to prepare them for perseverance in his service. He kept calling them to what was primary by means of what was secondary, that is, through foreshadowings to the reality, through things of time to the things of eternity, through things of the flesh to the things of the spirit, through earthly things to the heavenly things. As he said to Moses: You will fashion all things according to the pattern that you saw on the mountain.
For forty days Moses was engaged in remembering the words of God, the heavenly patterns, the spiritual images, the foreshadowings of what was to come. Saint Paul says: They drank from the rock that followed them, and the rock was Christ. After speaking of the things that are in the law he continues: All these things happened to them as symbols: they were written to instruct us, on whom the end of the ages has come.
Through foreshadowings of the future they were learning reverence for God and perseverance in his service. The law was therefore a school of instruction for them, and a prophecy of what was to come.
and to the Son
and to the Holy Spirit:
as it was in the beginning,
is now, and will be forever. Amen