And through the invocation the overshadowing power of the Holy Ghost becomes a rainfall for this new cultivation. For just as all things whatsoever God made he made by the operation of the Holy Ghost, so also it is by the operation of the Spirit that these things are done which surpass nature and cannot be discerned except by faith alone. “How shall this be done to me,” asked the blessed Virgin, “because I know not a man?” The archangel Gabriel answered, “The Holy Ghost shall come upon you, and the power of the Most High shall overshadow you.” And now you ask how the bread becomes the body of Christ and the wine and water the blood of Christ. And I tell you that the Holy Ghost comes down and works these things which are beyond description and understanding.

John of Damascus, Orthodox Faith 4.13, quoted in Arthur A Just (ed), Luke, Ancient Christian Commentary on Scripture, New Testament III, (Intervarsity Press, 2003) 19.