Elder Sophrony writes, "Scholars....have wrestled down the centuries trying to relate grace and the freedom of man. They forget, as it were, that there is another route to the solution of these problems--the way of existential knowledge of the reciprocity of the Divine grace and human freedom."
A key term used in the Greek Fathers is "proairesis" which means "faculty of free choice" or "deliberative choice." This emphasis on proairesis appears in such works as St. Gregory of Nyssa "Orations", St. John Chrysostom's "Sermons on St. Paul", as well as Maximus the Confessor and St. John of Damascus.
This goes hand-in-hand with the distinction made between "image" and "likeness" in the Church's interpretation of Genesis. St. Diadochos of Photike sums this up well when he writes "All of us who are human beings are in the image of God. But to be in his likeness belongs only to those who by great love have attached their freedom to God."
St. Mark the Ascetic writes, "Grace has been given mystically to those who have been baptized into Christ; and it becomes active in them to the extent that they actively observe the commandments."
Elder Sophrony again, summarizing St. Silouan the Athonite: "God constantly pursues man, and so soon as man manifests his own aspirations towards good and to putting good into actual practice, grace is already on the threshold. Yet the action or reaction of grace does not depend on man's will."
St. John Cassian's classic text "On Grace and Free Will" is good also. (He is *not* the founder of Semi-Peleganism and the Orthodox do not ascribe to this, as is so often misunderstood.)
Grace of course in these contexts does not mean "supernatural stuff" or something God gives us separate from Himself...rather, grace is always understood to be the very Uncreated Energies of God Himself. When we are given grace, we are in union with God "as far as we can bear it", as the troparian for the Feast of the Transfiguration teaches us.