For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God. 1 Corinthians 18
Every action, therefore, and performance of miracles by Christ are most great and divine and marvellous: but the most marvellous of all is His precious Cross. For no other thing has subdued death, expiated the sin of the first parent (5), despoiled Hades, bestowed the resurrection, granted the power to us of contemning the present and even death itself, prepared the return to our former blessedness, opened the gates of Paradise (6), given our nature a seat at the right hand of God, and made us the children and heirs of God (7), save the Cross of our Lord Jesus Christ. For by the Cross s all things have been made right. So many of us, the apostle says, as were baptized into Christ, were baptized into His death (9), and as many of you as have been baptized into Christ, have put on Christ (1). Further Christ is the power of God and the wisdom of God (2). Lo! the death of Christ, that is, the Cross, clothed us with the enhypostatic wisdom and power of God. And the power of God is the Word of the Cross, either because God’s might, that is, the victory over death, has been revealed to us by it, or because, just as the four extremities of the Cross are held fast and bound together by the bolt in the middle, so also by God’s power the height and the depth, the length and the breadth, that is, every creature visible and invisible, is maintained (3).
This was given to us as a sign on our forehead, just as the circumcision was given to Israel: for by it we believers are separated and distinguished from unbelievers.
Saint John of Damascus – An Exact Exposition of the Orthodox Faith