The Orthodox fathers use the sun as an analogy to the Holy and Divine Triad. The sun itself is the Heavenly Father. The light of the sun is the Divine Word and Son of God. The heat of the sun is the Holy Spirit.
No one can see the sun, except by the light, which enters our eyes and shows it to us. We have no other way to be in contact with the sun or even know for sure that it is there, but for the light (and the heat). If you approached the sun to touch it, you would be incinerated long before you reached it. The Father, thus, is ever intangible and unreachable to us, in His essence.
The light of the sun, though, both shows us what the sun looks like and tells us that it is there. ‘Who sees Me sees the Father,’ says Jesus, the Son and Word of God. In Jesus the Father is both visible and reachable. We make our prayers known to the Father through the Son. Moreover, light itself has two natures. It is both particles (photons) and waves (pure energy), and in the same way, Jesus the Son of God is both human and Divine. Yes, and He is the Phos ek Photós, ‘Light from Light.’
The heat of the sun would be evidence, even to a blind man, that the sun, or at least some source of heat, is out there, because he can feel its effect on him. In a similar way, even if a man is spiritually blind, he can still feel the warmth of the Holy Spirit falling on him, telling him that there is a Father in heaven, yet he can still move out of that sunlight and into the shadows. It is his choice.
There was never a sun without light and heat, yet the light is not the sun, nor is the heat the sun; each is distinct, yet inseparable from the source. In the same way, the Orthodox fathers teach that the Father is the source and principle of the Godhead, of the Divine Nature. The Son (only one of Him) is begotten eternally from the Father as light emanates eternally from the sun. As heat proceeds from the sun by means of the light that emanates from it, the Holy Spirit proceeds from the Father alone, but by means of the Son of God, who said, ‘I will ask the Father and He will send you another Advocate.’
Co-eternal, consubstantial—these are words that seem overpowering and mystery-laden, making the Holy Triad seem to be unthinkable and unexperienceable by man. But the Orthodox fathers show us that the mystery is not that God should be three yet one, but that we could have ever imagined a God who is only one.
The unity of the Divine Nature, ‘Hear, O Israel, Yahweh is our God, Yahweh is One’, is not diminished by His being a Triad. His Oneness is so One without second, so beyond numerical oneness, that even His triadic nature does not take away from it.
God is changeless, and yet He is One. God is changeless, and yet He is love. There can be no love except ‘between’ and no pure love, impartial and selfless love, except between ‘three.’ Hence, the Divine Nature says, ‘Let us make man in Our image.’
No one has ever seen God, only the Son of God, Jesus Christ, has made Him known and shown Him to us, being Himself God and yet not the Father. And the Holy Spirit, that third member of the One God in Triad, is our own membership in that Society of Persons which we call the Holy Trinity. Through Him, through the Spirit, we take our places at the banquet of the Divine Nature, becoming by genuine adoption what Christ is by nature, sons and daughters of the Most-High.
Théosis (divinization) is what we were made for, sotiría (salvation) is the process of our transfiguration.
Christ ‘was, is, and is to come.’
We were saved, are being saved, and are to be saved, that is, to be one with the Divine and Holy Triad, as Christ prays, ‘that they may be One, even as You, Father, and I are One.’
See the Orthodox ikon of the Holy Trinity, the original written by Andrei Rublev, posted above. There you will see the three ‘angels’ seated around a table, with one place left open for another.
That one is you.