When we speak about the reality of Christ's nature being in us, we would be speaking foolishly and impiously - had we not learned it from Him. ...And these elements (Body and Blood of Christ) bring it about, when taken and consumed, that we are in Christ and Christ is in us. Is this not true? Let those who deny that Jesus Christ is true God be free to find these things untrue. But He Himself is in us through the flesh and we are in Him, while that which we are with Him is in God.
St. John Chrysostom (PG 59:261)
This blood is the salvation of our soul; it cleanses our souls, it beautifies our soul; ... it makes it shine even more than gold. Through the pouring out of this blood, it becomes possible to walk the path of heaven.
St. Augustine, Sermons, [227] A.D. 391-430:
That Bread which you see on the altar, having been sanctified by the word of God, is the Body of Christ. That chalice, or rather, what is in that chalice, having been sanctified by the word of God, is the Blood of Christ. Through that bread and wine the Lord Christ willed to commend His Body and Blood, which He poured out for us unto the forgiveness of sins. If you receive worthily, you are what you have received.
St. Cyril of Alexandria, Commentary on the Gospel of Matthew 26,27, 428 A.D.:
Christ said indicating (the bread and wine): 'This is My Body,' and `This is My Blood,' in order that you might not judge what you see to be a mere figure. The offerings, by the hidden power of God Almighty, are changed into Christ's Body and Blood, and by receiving these we come to share in the life-giving and sanctifying efficacy of Christ.