“The grace of the New Testament is mystically hidden in the letter of the Old.” (St. Maximos the Confessor, The Philokalia, Loc. 14653)
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Clearly the Church Fathers saw all of the Scriptures as essential. The Old Testament bore witness to Christ. The New Testament was hidden in the text of the Old Testament. The New Testament revealed the meaning of the Old Testament. Christ who was but a shadow in the Old Testament, now is fully revealed in the New. You cannot completely understand either Covenant without the other.
We have already encountered how Jesus read and understood the Old Testament:
Jesus said: “You search the scriptures, because you think that in them you have eternal life; and it is they that bear witness to me; yet you refuse to come to me that you may have life. I do not receive glory from men. But I know that you have not the love of God within you. I have come in my Father’s name, and you do not receive me; if another comes in his own name, him you will receive. How can you believe, who receive glory from one another and do not seek the glory that comes from the only God? Do not think that I shall accuse you to the Father; it is Moses who accuses you, on whom you set your hope. If you believed Moses, you would believe me, for he wrote of me. But if you do not believe his writings, how will you believe my words?” (John 5: 39-47)
And he said to them, “O foolish men, and slow of heart to believe all that the prophets have spoken! Was it not necessary that the Christ should suffer these things and enter into his glory?” And beginning with Moses and all the prophets, he interpreted to them in all the scriptures the things concerning himself. . . . Then he said to them, “These are my words which I spoke to you, while I was still with you, that everything written about me in the law of Moses and the prophets and the psalms must be fulfilled.” (Luke 24:25-27, 44)

Our Lord Jesus Christ had no doubt that the Old Testament was written about Him, and that Moses and all the prophets were writing about the Messiah when they presented the prophecies and promises of God. So too, St. Cyril of Jerusalem writing in the 4th Century says:
“Pass from the old to the new, from the figure to the reality. There Moses was sent by God to Egypt; here Christ is sent from the Father into the world. Moses’ mission was to lead a persecuted people out of Egypt; Christ’s, to rescue all the people of the world who were under the tyranny of sin. There the blood of a lamb was the charm against the destroyer; here, the blood of the unspotted Lamb, Jesus Christ, is appointed your inviolable sanctuary against demons. Pharaoh pursued that people of old right into the sea; this outrageous spirit [i.e., Satan], the impudent author of all evil, followed each of you up to the very verge of the saving streams [i.e., your baptisms]. That other tyrant is engulfed and drowned in the Red Sea; this one is destroyed in the saving water.” (A Patristic Treasury: Early Church Wisdom for Today, Kindle Loc. Loc. 3540-45)
The stories and history of the Old Testament prefigure Christ, to make the Messiah visible and recognizable. The narrative of the Old Testament helps us to understand who Jesus is and how He is bringing about the salvation of the world. St. Maximos the Confessor who like all Fathers expounded on the Scriptures said:
“The Law is the shadow of the Gospel. The Gospel is the image of the blessings held in store. The Law checks the actualization of evil. The Gospel brings about the realization of divine blessings.” (The Philokalia, Loc. 14659-62)
St Maximos reads Zechariah 4:1-4 –
“And the angel who talked with me came again, and waked me, like a man that is wakened out of his sleep. And he said to me, “What do you see?” I said, “I see, and behold, a lampstand all of gold, … And there are two olive trees by it, one on the right of the bowl and the other on its left.”
Maximos comments:
I think that the olive tree on the left side of the candlestick signifies the Old Testament, in which the emphasis is mainly on practical philosophy; while that on the right signifies the New Testament, which teaches a new revelation and brings each believer to a state of contemplation. The first supplies the qualities of virtue, the second the principles of spiritual knowledge to those who meditate on what is divine. The first clears away the mist of visible things and raises the intellect to realities that are akin to it when it is purged of all material fantasies. The second purifies the intellect of its attachment to materiality, with resolute strength knocking out as though with a hammer the nails that rivet will and disposition to the body.” (THE PHILOKALIA, Kindle Loc. 19193-99)
Both Covenants are needed to understand either of them. The Old and the New are vitally linked together for our salvation. St. Maximos continues:
“The Old Testament makes the body obedient to the intelligence and raises it towards the soul by means of the virtues, preventing the intellect from being dragged down towards the body. The New Testament fires the intellect with love and unites it to God. Thus the Old Testament makes the body one in its activity with the intellect; the New Testament makes the intellect one with God through the state of grace. So close is the likeness to God which the intellect acquires, that God, who is not known as He is by nature in Himself to anyone in any way at all, is known through it just as an archetype is known from an image. Since the Old Testament is a symbol of the practice of the virtues, it brings the body’s activity into harmony with that of the intellect. Since the New Testament confers contemplation and spiritual knowledge, it illumines with divine intellections and gifts of grace the intellect that cleaves to it mystically. The Old Testament supplies the man of spiritual knowledge with the qualities of virtue; the New Testament endows the man practicing the virtues with the principles of true knowledge.” (THE PHILOKALIA, Kindle Loc. 19199-209)
We only can grow spiritually when we properly read and comprehend both Testaments together. The Old can be properly understood only in and through the New Testament. The New not only fulfills the Old but also explains its purpose and mission. The New Testament however does not point back to the Old, but rather in Christ points to the eschaton – to the Kingdom of Heaven yet to come
“Just as the teachings of the Law and the prophets, being harbingers of the coming advent of the Logos in the flesh, guide our souls to Christ (cf. Gal. 3:24), so the glorified incarnate Logos of God is Himself a harbinger of His spiritual advent, leading our souls forward by His own teachings to receive His divine and manifest advent. He does this ceaselessly, by means of the virtues converting those found worthy from the flesh to the spirit. And He will do it at the end of the age, making manifest what has hitherto been hidden from all men.” (St. Maximos the Confessor, The Philokalia, Loc. 15042-50)
Next in the series: Christ in the Old Testament