Man, however, being endowed with reason and free will, received the power of continuous union with God through his own choice – if, indeed, he should abide in goodness, that is, in obedience to his Maker.

However, man transgressed the command of his Creator and became liable to death and corruption.

Therefore the Creator and Maker of our race, because of His bowels of compassion, took on our likeness, becoming man in all things but without sin, and was united to our nature (Heb. 2:17).

For since He bestowed on us His own image and His own spirit and we did not keep them safe, He took Himself a share in our poor and weak nature, in order that He might cleanse us and make us incorruptible, and establish us once more as partakers of His divinity.

[...] Through His birth, that is, His incarnation, and baptism and passion and resurrection, He delivered our nature from the sin of our first parent and death and corruption.

He became the first-fruits of the resurrection, and made Himself the way and image and pattern, in order that we, too, following in His footsteps, may become by adoption what He is Himself by nature (Rom. 7:17) – sons and heirs of God and joint heirs with Him.

We who are born of Adam are in his image and are the heirs of the curse and corruption.

Therefore Christ gave us a second birth in order that, being born of Him, we may be in His likeness, and may be heirs of His incorruption and blessing and glory.

[...] The bread itself and the wine are changed into God’s body and blood.

If you enquire how this happens, it is enough for you to learn that it was through the Holy Spirit, just as the Lord took on Himself flesh that subsisted in Him and was born of the holy Mother of God through the Spirit.

And we know nothing further save that the Word of God is true and energises and is omnipotent, but the manner of this cannot be searched out.

[...] The bread of the table and the wine and water are supernaturally changed by the invocation and presence of the Holy Spirit into the body and blood of Christ, and are not two but one and the same.

Wherefore to those who partake worthily with faith, it is for the remission of sins and for life everlasting and for the safeguarding of soul and body. But to those who partake unworthily without faith, it is for chastisement and punishment.

The death of the Lord became to those who believe life and incorruption for the enjoyment of eternal blessedness.

John Damascene (c.675-749): De Fide Orthodoxa 4, 13.