What did St. Gregory of Nazianzus mean by forbidden knowledge and the need to conceal knowledge gained within the Church?

In Oration 40, towards the end, a translation from newadvent.org is as follows: > But not yet perhaps is there formed upon your soul any writing good or > bad; and you want to be written upon today, and formed by us unto > perfection. Let us go within the cloud. Give me the tables of your > heart; I will be your Moses, though this be a bold thing to say; I > will write on them with the finger of God a new Decalogue. Exodus > 38:28 I will write on them a shorter method of salvation. And if there > be any heretical or unreasoning beast, let him remain below, or he > will run the risk of being stoned by the Word of truth. I will baptize > you and make you a disciple in the Name of the Father and of the Son > and of the Holy Ghost; and These Three have One common name, the > Godhead. And you shall know, both by appearances Matthew 28:19 and by > words that you reject all ungodliness, and are united to all the > Godhead. Believe that all that is in the world, both all that is seen > and all that is unseen, was made out of nothing by God, and is > governed by the Providence of its Creator, and will receive a change > to a better state. Believe that evil has no substance or kingdom, > either unoriginate or self-existent or created by God; but that it is > our work, and the evil one's, and came upon us through our > heedlessness, but not from our Creator. Believe that the Son of God, > the Eternal Word, Who was begotten of the Father before all time and > without body, was in these latter days for your sake made also Son of > Man, born of the Virgin Mary ineffably and stainlessly (for nothing > can be stained where God is, and by which salvation comes), in His own > Person at once entire Man and perfect God, for the sake of the entire > sufferer, that He may bestow salvation on your whole being, having > destroyed the whole condemnation of your sins: impassible in His > Godhead, passible in that which He assumed; as much Man for your sake > as you are made God for His. Believe that for us sinners He was led to > death; was crucified and buried, so far as to taste of death; and that > He rose again the third day, and ascended into heaven, that He might > take you with Him who were lying low; and that He will come again with > His glorious Presence to judge the quick and the dead; no longer > flesh, nor yet without a body, according to the laws which He alone > knows of a more godlike body, that He may be seen by those who pierced > Him, Revelation 1:7 and on the other hand may remain as God without > carnality. Receive besides this the Resurrection, the Judgment and the > Reward according to the righteous scales of God; and believe that this > will be Light to those whose mind is purified (that is, God — seen and > known) proportionate to their degree of purity, which we call the > Kingdom of heaven; but to those who suffer from blindness of their > ruling faculty, darkness, that is estrangement from God, proportionate > to their blindness here. Then, in the tenth place, work that which is > good upon this foundation of dogma; for faith without works is dead, > James 2:17 even as are works apart from faith. This is all that may be > divulged of the Sacrament, and that is not forbidden to the ear of the > many. The rest you shall learn within the Church by the grace of the > Holy Trinity; and those matters you shall conceal within yourself, > sealed and secure. At the end of this paragraph there is a reference to knowledge only gained after initiation into the Church, and of the need to conceal that knowledge. What could St. Gregory have been talking about? I noticed that in this creed of sorts Gregory does not talk about Communion - could it be that the Eucharist, and the mystery of eating the flesh of Christ, was the mystery that Christians could not speak about to outsiders/the uninitiated? The one reference I have found in that oration to the Eucharist is a somewhat vague > Remember how poor you once were, and how rich you were made. One in > want of bread or of drink, perhaps another Lazarus, is cast at your > gate; respect the Sacramental Table to which you have approached, the > Bread of Which you have partaken, the Cup in Which you have > communicated, being consecrated by the Sufferings of Christ. As this oration appears to be directed to those about to undergo the Sacrament of Baptism, this could still fit in with my theory that the true "trans-subtantiated" nature of the Bread and Cup that is celebrated before the Sacramental Table is only revealed to the initiated. A further side note or post scriptum - what does St. Gregory mean by the "Festival on the illustrious Day of the Holy Lights"?