The Vision and Contemplation of God
According to ancient Greek philosophy, the highest good, the greatest state of true happiness, was when the innermost part of the human soul contemplated and was illuminated by the divine. The ultimate goal of human existence was for the soul/spirit to conform itself to the divine archetype by having a constant vision of the divine before it, and through its focused gaze on the nature of the divine the soul would gain immortality and the divine likeness. This concept of a mystic, direct and intimate union of the soul with God through contemplation or ecstasy was hugely influential within Greek philosophy and was expounded by Plato, Aristotle, Middle-Platonism and Neo-Platonism. As a result it exercised a profound influence on Greek-Christian thought, especially on Christians who had philosophical training.
In the second century AD, Christian Apologists when speaking of how Christ taught Monotheism and God's moral laws, draw on the language of philosophy to speak of how Christ was the "logos" (a word from Greek philosophy that described the mediator of divine illumination) who has brought this "knowledge of God". Toward the end of the second century this gets taken to an extreme by Irenaeus and Clement of Alexandria who draw fully on the Greek philosophical conception of union with God. For Clement the highest possible good is "divine contemplation and illumination", and Christ's illuminating teachings are the instruction through which an initiate can attain to the true vision of the divine nature and live a contemplative life. Clement sees a great difference between the average Christian who merely does what God wants and the super-Christian who fully apprehends the reality of the divine through contemplation. For Irenaeus "union and communion between God and man" is the highest goal and the divine incarnation in the person of Jesus that opened the way to unite the human soul with the divine. These ideas also play a prominant role in the fourth to sixth centuries AD, heavily influencing theologians such as Athanasius, Augustine, the Cappadocians, Maximus etc.
In Christian theology there are essentially three variant forms of this idea which are significantly different to each other and worth dealing with separately:
1. Jesus is conceived of a teacher and revealer of truth about God. He teaches monotheism, God's commandments, morality etc. By following the teachings and example of Jesus a person can live a morally virtuous life. God will reward such people with immortality. Language from Greek philosophy is used to describe these concepts.
2. The mystic vision of the divine light, and conformity of the soul to the likeness of the divine is the highest goal and state of the soul. To set ones gaze upon the divine results in moral behavior and godliness being manifested in one's life, and brings immortality to the soul by virtue of its direct mystical participation within the immortal divine nature. Jesus taught information about God and mystical truths about the divine nature. Through the incarnation, the nature of God is revealed and by contemplation of the person of Jesus as the incarnate God we can contemplate the divine nature.
3. Human souls due to their separation from the divine essence and light have lost their similitude to the divine and become subject to corruption. Human souls will eventually pass into non-existence due to this ever-increasing decay unless reunited with the divine. In the incarnation God mystically joined the divine essence and the created order, making them one in the God-human Jesus. By that act all humanity was reconnected to the divine and the decay into non-existence of the human soul averted.
Those three ways of thinking in order represent an increasing influence of Greek philosophical concepts on Christianity. In the first, philosophical terms are used to describe Christian doctrine without any of the philosophical concepts being present. In the second, many concepts from Greek philosophy are taken for granted and Christianity is seen as the best means to attaining the goal of the philosopher. In the third, concepts from Greek philosophy map out the 'problem' that faces humanity and are used to dictate the understanding of its solution in Christ. All three concepts are present strongly in Athanasius' influential work On the Incarnation of the Word (~318AD) and continued to play a strong role through the centuries. (eg In the fourteenth century it was suggested that the use of meditation, repetition and breathing by monks to attain an inner vision and experience of the ineffable uncreated divine light in the union of their consciousness with the divine energies was a waste of time, but church councils ruled on it as a worthwhile activity.)