You
ask how the bread becomes the Body of Christ, and the wine. . . the
Blood of Christ. I shall tell you: the Holy Spirit comes upon them
and accomplishes what surpasses every word and thought. . . . Let it
be enough for you to understand that it is by the Holy Spirit, just
as it was of the Holy Virgin and by the Holy Spirit that the Lord,
through and in Himself, took flesh.
--
Saint John of Damascus