For Christ is the treasure which was hid in the field (Matt. 13:44), that is, in this world – for “the field is the world” (Matt. 13:38).
But the treasure hid in the Scriptures is Christ, since He was pointed out by means of types and parables.
Hence His human nature could not be understood, prior to the consummation of those things which had been predicted, that is, the advent of Christ.
And therefore it was said to Daniel the prophet:
“Shut up the words, and seal the book even to the time of consummation, until many learn, and knowledge be completed. For at that time, when the dispersion shall be accomplished, they shall know all these things” (Dan. 12:4, 7).
Jeremiah also says, “In the last days they shall understand these things” (Jer. 23:20).
For every prophecy, before its fulfilment, is to men full of enigmas and ambiguities. But when the time has arrived, and the prediction has come to pass, then the prophecies have a clear and certain exposition.
[…] When…the law is read to the Jews, it is like a fable; for they do not possess the explanation of all things pertaining to the advent of the Son of God, which took place in human nature.
But when it is read by the Christians, it is a treasure, hid indeed in a field, but brought to light by the Cross of Christ, and explained.
It enriches the understanding of men, showing forth the wisdom of God and declaring His dispensations with regard to man.
It forms the kingdom of Christ beforehand, preaching by anticipation the inheritance of the holy Jerusalem,
It proclaims beforehand that the man who loves God shall arrive at such excellency as even to see God, and hear His word, and from the hearing of His discourse be glorified to such an extent, that others cannot behold the glory of his countenance, as was said by Daniel:
“Those who do understand, shall shine as the brightness of the firmament, and many of the righteous as the stars forever and ever” (Dan. 12:3).
Thus, then, I have shown it to be, if any one read the Scriptures.
For thus it was that the Lord discoursed with the disciples after His resurrection from the dead, proving to them from the Scriptures themselves “that Christ must suffer, and enter into His glory, and that remission of sins should be preached in His name throughout all the world” (Luke 24: 26, 47).
And the disciple will be perfected, and rendered like the householder, “who bringeth forth from his treasure things new and old” (Matt. 13:52).
Irenaeus of Lyons (2nd century AD – c. 202): Adversus Haereses 4,26,1 (slightly adapted)