The rise and fall, ebb and flow, wax and wane of Christian spirituality is that of progression towards union. Jesus, the first born among brothers, is the perfect union of divinity and humanity. As Saint Augustine said, "God became man so that man might become God." Don't misunderstand this statement, it is not some new age belief that each of us are gods. This statement, taken in context, speaks towards the potential of man as he humbles himself before the majesty of God.
The ancient Christian mystics called the journey towards union with God theosis, divinization, and deification. Today we use terms like transformation, sanctification, or spiritual formation. The great spiritual writers of our history mined the depths of verses like these:
“He who is joined to the Lord is one spirit with Him.” 1 Corinthians 6:17
“…by these you might be partakers of the divine nature…” 2 Peter 1:4
Influential authors like Maximos the Confessor, Bernard of Clairvaux, Thomas Aquinas and John of the Cross understood the mystery of the Divine Union as a union of wills. We were to be so united to God that our hearts became a reflection of his will. This was accomplished by routinely laying down their lives, and a direct application of that was an intense devotional life. It was demonstrated in living a life devoted to knowing He who is Light.
In early Christianity, men and women fled the pagan societies of the day for the desert to know this God in the inner sanctum of the heart. The great historical figures in Christian history saw Psalm 36:9 as reality,
“For with you is the fountain of life; in your light we see light.”
This was not viewed as merely a doctrinal truth, but an experiential reality.
As a Christian, and bearer of He who is Light, you are destined to experience this Light. This is such a foundational truth regarding Christian spirituality that anyone who calls themselves a Christian yet does not have a conversational relationship with God is experiencing an abrogated version of what they claim to be living.
Mankind has been made to be partakers of the divine nature. Adam and Eve began this journey when they were told,
"Be fruitful and multiply, fill the earth and subdue it, and have dominion over the fish of the sea and over the birds of the heavens and over every living thing that moves on the earth."
God had done just that in the first few days of creation. He multiplied the heavens and earth when he separated them by the expanse between them, he spoke and the oceans increased, the animals sprung forth; mountains, hills, and valleys were formed. Adam and Eve walked with the God who is light, they ate of his life, and they were commanded to take up the role he began by continually filling the earth. Of course, we all know what happened. Adam and Eve ate of the tree of the knowledge of good and evil and the rest lies in the annuls of history.
Ultimately, “be fruitful and multiply and fill the earth and subdue it” found its fulfillment in Jesus, who is the true picture of divinity united with humanity. He brings forward the command to Adam and Eve in Genesis into the New Testmanet by saying,
"Go therefore and make disciples of all nations," as well as, "Go into all the world and proclaim the gospel to the whole creation."
This is multiplication (make disciples) and subduing (proclaim the gospel).
What did Jesus do as the one who was fully divine and fully human? He made disciples and proclaimed the gospel. You are made in the image of the God who is light. You are to grow in this light, and as you grow you will partake in the very nature of God. This is a mystery.
Eve was created in the image of Adam, which he recognized when he said, "This is at last bone of my bone and flesh of my flesh." Their likeness granted them the ability to unite. This initial uniting was found in physical intimacy. Similarity of image brought an ability to unite, as man and woman complement each other.
During creation, God established this principle when he said,
"Let the earth bring forth living creatures according to their kinds—livestock and creeping things and beasts of the earth according to their kinds."
It is kind that finds union with kind. In the same way man is made in God's image. As the image bearers of God, man has been granted the ability to unite with God.
Your spirit is the receptacle of God's light. When God created man, he granted him the capacity to contain His Spirit. No other being exists that has this capacity, man is unique in his relationship to his Creator. Man is created in the image of God. While creation brings God pleasure by simply being, mankind brings God pleasure by becoming. Peter echoes this refrain by proclaiming this mystery, that mankind has been made to be "partakers in the divine nature."