ST. GREGORY OF NYSSA (c. 335 - 394 A.D.)
This Body, by the indwelling of God the Word, has been made over to divine dignity. Rightly then, do we believe that the bread consecrated by the word of God has been made over into the Body of God the Word. For that Body was, as to its potency, bread; but it has been consecrated by the lodging there of the Word, who pitched His tent in the flesh. From the same cause, therefore, by which the bread that was made over into that Body is made to change into divine strength, a similar result now takes place. As in the former case, in which the grace of the Word made holy that body the substance of which is from bread, and in a certain manner is itself bread, so in this case too, the bread, as the Apostle says, "is consecrated by God's word and by prayer"; not through its being eaten does it advance to become the Body of the Word, but it is made over immediately into the Body by means of the word, just as was stated by the Word, "This is My Body!" ...In the plan of His grace He spreads Himself to every believer by means of that Flesh, the substance of which is from wine and bread, blending Himself with the bodies of believers, so that by this union with the Immortal, man, too, may become a participant in incorruption. These things He bestows through the power of the blessing which transforms the nature of the visible things to that [of the Immortal]. (The Great Catechism 37)
sursa:
http://www.bringyou.to/apologetics/num8.htm