I will remind you again about Illuminations, and that often, and will reckon them up from Holy Scripture. For I myself shall be happier for remembering them (for what is sweeter than light to those who have tasted light?) and I will dazzle you with my words. "There is sprung up a light for the righteous, and its partner joyful gladness" (Ps. 97:11). And, "The light of the righteous is everlasting" (Prov. 13:9)... And you have heard David's words; "The Lord is my Light and my Salvation, whom then shall I fear?" (Ps. 27:1). And now {David} asks that the Light and the Truth may be sent forth for him (Ps. 43:3), now giving thanks that he has a share in it, in that the Light of God is marked upon him; that is, that the signs of the illumination given are impressed upon him and recognized.
(Oration 40:36)
Now, we come to another action of Christ, and another mystery. I cannot restrain my pleasure; I am rapt into God... Christ is illumined, let us shine forth with Him.
(Oration 39:14)
God is Light... presenting Himself to our minds in proportion as we are cleansed; and loved in proportion as He is presented to our mind... and pouring Himself out upon what is external to Him. That Light, I mean, which is contemplated in the Father and the Son and the Holy Ghost, Whose riches is Their unity of nature, and the one outleaping of Their brightness.
(Oration 40:5)
For where fear is, there is keeping of commandments; and where there is keeping of commandments there is purifying of the flesh, that cloud which covers the soul and suffers it not to see the Divine Ray. And where there is purifying there is Illumination; and Illumination is the satisfying of desire to those who long for the greatest things, or the Greatest Thing, or That Which surpasses all greatness.
(Oration 39:8)
Whoever has been permitted to escape by reason and contemplation from matter and this fleshly cloud or veil (whichever it should be called) and to hold communion with God, and be associated, as far as man's nature can attain, with the purest Light, blessed is he, both from his ascent from hence, and for his deification there, which is conferred by true philosophy, and by rising superior to the dualism of matter, through the unity which is perceived in the Trinity.
(Oration 43:2)
...the mind should retire into itself, and recall its powers from sensible things, in order to hold pure communion with God, and be clearly illumined by the flashing rays of the Spirit, with no admixture or disturbance of the divine light by anything earthly or clouded, until we come to the source of the effulgence which we enjoy here, and regret and desire are alike stayed, when our mirrors pass away in the light of truth.
(Oration 12:4)
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... This is all that may be divulged of the Sacrament {of Baptism}, 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.
(Oration 40:45)
{On the baptism of the father of Gregory of Nazianzus, who was also named Gregory:}
And as he was ascending out of the water, there flashed around him a light and a glory worthy of the disposition with which he approached the girt of faith; this was manifest even to some others, who for the time concealed the wonder, from fear of speaking of a sight which each one thought had been only his own, but shortly afterwards communicated it to one another. To the baptiser and initiator, however, it was so clear and visible, that he could not even hold back the mystery, but publicly cried out that he was anointing with the Spirit his own successor.
(Oration 18:13)