The sign of the cross is the most frequently used sacramental of the Church. The sign is a repetition in motion of the symbol of our salvation, the cross on which Christ died. The sign of the cross is made during the Mass, at blessings and generally at the opening and closing of prayer.
St. Cyril of Jerusalem, 315 – 386 had written, “Let us not then be ashamed to confess the Crucified. Be the Cross our seal made with boldness by our fingers on our brow and in everything; over the bread we eat, and the cups we drink; in our comings in, and goings out; before our sleep, when we lie down and when we awake; when we are in the way and when we are still.”
God speaking, through Ezekiel, to the remnant of Israel, tells the faithful: “And the Lord said to him: Go through the midst of the city, through the midst of Jerusalem: and mark a Tau (the Hebrew symbol “x” or “+”) upon the foreheads of the men that sigh, and mourn for all the abominations that are committed in the midst thereof” (Ezekiel 9:4).
The Catholic Sign of the Cross is absolutely ancient, rooted not only in the Old Testament but the New Testament (the Book of Revelation, written around 100, speaks of those who have the sign of God on their foreheads).
When Catholics undergo the Sacrament of Confirmation, the Bishop (sometimes a priest) seals the sign on our foreheads with holy Chrism.
St. John of Damascus, d. 749, wrote: “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.”
The Christian sign of the cross was originally made in some parts of the Christian world with the right-hand thumb across the forehead only. In other parts of the early Christian world it was done with the whole hand or with two fingers.
Around the year 200 in Carthage (modern Tunisia, Africa), Tertulian says: “We Christians wear out our foreheads with the sign of the cross.” Vestiges of this practice remain: Catholics sign a cross on their forehead before hearing the Gospels during Mass; foreheads are marked with an ash cross on Ash Wednesday.
By the fourth century, the sign of the cross involved other parts of the body beyond the forehead. (8:2)