An Explanation of the Bread, Wine, and Water Offering at the Proskomedia Service Before the Divine Liturgy
by St. Germanus of Constantinople
from his commentary On the Divine Liturgy, translated by Paul Meyendorff, St. Vladimir's Seminary Press, 1984, p. 71.
The bread of offering [offered by our prosfora bakers], which is purified, signifies the superabundant riches of the goodness of our God, because the Son of God became man and gave Himself as an offering and oblation in ransom and atonement for the life and salvation of the world He assumed the entirety of human nature, except for sin. He offered Himself as first-fruits and chosen whole burnt-offering to the God and Father on behalf of the human race, as is written: 'I am the bread which came down from heaven,” and 'He who eats this bread will live for ever' (Jn. 6:51). About this the Prophet Jeremiah says: 'Come, let us place a stake in his bread' (11:19 LXX), point to the wood of the cross nailed to His body.
The piece which is cut out [of the loaf] with the lance [by the priest] signifies that 'Like a sheep He is led to the slaughter, and like a lamb that before its shearer is dumb' (cf. Is. 54:7).