Clement of Alexandria, Stromata 5:10
It is stated that mysteries were given by the Lord to His Apostles, and have been “concealed” within the Old Testament. Reason for secrecy is also explained (p. 1)
Translation – Philip Schaff, The Apostolic Fathers.
Retrieved from http://www.earlychristianwritings.com/text/clement-stromata-book5.html on August 11, 2015
Rightly, therefore, the divine apostle says, "By revelation the mystery was made known to me (as I wrote before in brief, in accordance with which, when ye read, ye may understand my knowledge in the mystery of Christ), which in other ages was not made known to the sons of men, as it is now revealed to His holy apostles and prophets." For there is an instruction of the perfect, of which, writing to the Colossians, he says, "We cease not to pray for you, and beseech that ye may be filled with the knowledge of His will in all wisdom and spiritual understanding; that ye may walk worthy of the Lord to all pleasing; being fruitful in every good work, and increasing in the knowledge of God; strengthened with all might according to the glory of His power." And again he says, "According to the disposition of the grace of God which is given me, that ye may fulfil the word of God; the mystery which has been hid from ages and generations, which now is manifested to His saints: to whom God wished to make known what is the riches of the glory of this mystery among the nations." So that, on the one hand, then, are the mysteries which were hid till the time of the apostles, and were delivered by them as they received from the Lord, and, concealed in the Old Testament, were manifested to the saints. And, on the other hand, there is "the riches of the glory of the mystery in the Gentiles," which is faith and hope in Christ; which in another place he has called the "foundation." And again, as if in eagerness to divulge this knowledge, he thus writes: "Warning every man in all wisdom, that we may present every man (the whole man) perfect in Christ;" not every man simply, since no one would be unbelieving. Nor does he call every man who believes in Christ perfect; but he says all the man, as if he said the whole man, as if purified in body and soul. For that the knowledge does not appertain to all, he expressly adds: "Being knit together in love, and unto all the riches of the full assurance of knowledge, to the acknowledgment of the mystery of God in Christ, in whom are hid all the treasures of wisdom and of knowledge." "Continue in prayer, watching therein with thanksgiving." And thanksgiving has place not for the soul and spiritual blessings alone, but also for the body, and for the good things of the body. And he still more clearly reveals that knowledge belongs not to all, by adding: "Praying at the same time for you, that God would open to us a door to speak the mystery of Christ, for which I am bound; that I may make it known as I ought to speak." For there were certainly, among the Hebrews, some things delivered unwritten. "For when ye ought to be teachers for the time," it is said, as if they had grown old in the Old Testament, "ye have again need that one teach you which be the first principles of the oracles of God; and are become such as have need of milk, and not of solid food. For every one that par-taketh of milk is unskilful in the word of righteousness; for he is a babe, being instructed with the first lessons. But solid food belongs to those who are of full age, who by reason of use have their senses exercised so as to distinguish between good and evil. Wherefore, leaving the first principles of the doctrine of Christ, let us go on to perfection."
Barnabas, too, who in person preached the word along with the apostle in the ministry of the Gentiles, says, "I write to you most simply, that ye may understand." Then below, exhibiting already a clearer trace of gnostic tradition, he says, "What says the other prophet Moses to them? Lo, thus saith the Lord God, Enter ye into the good land which the Lord God sware, the God of Abraham, and Isaac, and Jacob; and ye received for an inheritance that land, flowing with milk and honey. What says knowledge? Learn, hope, it says, in Jesus, who is to be manifested to you in the flesh. For man is the suffering land; for from the face of the ground was the formation of Adam. What, then, does it say in reference to the good land, flowing with milk and honey? Blessed be our Lord, brethren, who has put into our hearts wisdom, and the understanding of His secrets. For the prophet says, "Who shall understand the Lord's parable but the wise and understanding, and he that loves his Lord?" It is but for few to comprehend these things. For it is not in the way of envy that the Lord announced in a Gospel, "My mystery is to me, and to the sons of my house;" placing the election in safety, and beyond anxiety; so that the things pertaining to what it has chosen and taken may be above the reach of envy. For he who has not the knowledge of good is wicked: for there is one good, the Father; and to be ignorant of the Father is death, as to know Him is eternal life, through participation in the power of the incorrupt One. And to be incorruptible is to participate in divinity; but revolt from the knowledge of God brings corruption. Again the prophet says: "And I will give thee treasures, concealed, dark, unseen; that they may know that I am the Lord."
Similarly David sings: "For, lo, Thou hast loved truth; the obscure and hidden things of wisdom hast Thou showed me." "Day utters speech to day" (what is clearly written), "and night to night proclaims knowledge" (which is hidden in a mystic veil); "and there are no words or utterances whose voices shall not be heard" by God, who said, "Shall one do what is secret, and I shall not see him?"
Wherefore instruction, which reveals hidden things, is called illumination, as it is the teacher only who uncovers the lid of the ark, contrary to what the poets say, that "Zeus stops up the jar of good things, but opens that of evil." "For I know," says the apostle, "that when I come to you, I shall come in the fulness of the blessing of Christ;" designating the spiritual gift, and the gnostic communication, which being present he desires to impart to them present as "the fulness of Christ, according to the revelation of the mystery sealed in the ages of eternity, but now manifested by the prophetic Scriptures, according to the command of the eternal God, made known to all the nations, in order to the obedience of faith," that is, those of the nations who believe that it is. But only to a few of them is shown what those things are which are contained in the mystery. Rightly then, Plato, in the Epistles, treating of God, says: "We must speak in enigmas that should the tablet come by any mischance on its leaves either by sea or land, he who reads may remain ignorant." For the God of the universe, who is above all speech, all conception, all thought, can never be committed to writing, being inexpressible even by His own power. And this too Plato showed, by saying:
"Considering, then, these things, take care lest some time or other you repent on account of the present things, departing in a manner unworthy. The greatest safeguard is not to write, but learn; for it is utterly impossible that what is written will not vanish."
Akin to this is what the holy Apostle Paul says, preserving the prophetic and truly ancient secret from which the teachings that were good were derived by the Greeks: "Howbeit we speak wisdom among them who are perfect; but not the wisdom of this world, or of the princes of this world, that come to nought; but we speak the wisdom of God hidden in a mystery." Then proceeding, he thus inculcates the caution against the divulging of his words to the multitude in the following terms: "And I, brethren, could not speak to you as to spiritual, but as to carnal, even to babes in Christ. I have fed you with milk, not with meat: for ye were not yet able; neither are ye now able. For ye are yet carnal."
If, then, "the milk" is said by the apostle to belong to the babes, and "meat" to be the food of the full-grown, milk will be understood to be catechetical instruction -- the first food, as it were, of the soul. And meat is the mystic contemplation; for this is the flesh and the blood of the Word, that is, the comprehension of the divine power and essence. "Taste and see that the Lord is Christ," it is said. For so He imparts of Himself to those who partake of such food in a more spiritual manner; when now the soul nourishes itself, according to the truth-loving Plato. For the knowledge of the divine essence is the meat and drink of the divine Word. Wherefore also Plato says, in the second book of the Republic, "It is those that sacrifice not a sow, but some great and difficult sacrifice," who ought to inquire respecting God. And the apostle writes, "Christ our passover was sacrificed for us;" -- a sacrifice hard to procure, in truth, the Son of God consecrated for us.