The original practice seems to have involved simply making the sign of the cross on one’s own forehead with the thumb. There is no way to determine exactly when the larger crossing (forehead, navel or lower chest, and shoulders) came into use. But the leap from the smaller to the larger is of little consequence because the symbolism is still the same. Let’s observe the sign of the cross in the Early Church Fathers.
Tertullian, known as the founder of Latin Christianity, speaks of the sign of the cross in The Chaplet.
At every forward step and movement, at every going in and out, when we put on our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign. [ANF 3: 94-5, ch. 3]
St. Hippolytus of Rome speaks of the same in On the Apostolic Tradition.
If you are tempted, seal your foreheads reverently. For this is the Sign of the
Passion, displayed and made manifest against the devil, provided that you do it with faith,
not to be seen by men, but by presenting it with skill like a shield.
2Because the Adversary, when he sees the strength of the heart and when he sees the inner
man which is animated by the Word show, formed on the exterior, the interior image of the
Word, he is made to flee by the Spirit which is in you. 3This is symbolized by the Paschal
lamb which was sacrificed, the blood of which Moses sprinkled on the threshold, and
smeared on the doorposts. He told us of the faith which is now in us, which was given to
us through the perfect Lamb.
4By sealing the forehead and eyes with the hand, we turn aside the one who is seeking to destroy us. [from http://www.bombaxo.com/hippolytus.html, tr. Kevin P. Edgecomb, ch. 42]
The power of the sign is very powerfully spelled out by Hippolytus here. It is to be noted, however, that he is adamant that one must “do it with faith” to make it effectual. Then again, that is true of any religious action for as the Apostle Paul tells us, “whatever does not proceed from faith is sin.” (Romans 14: 23 RSV)
Saint Athanasius, the great defender of orthodox Christology, also speak of the power of this sign.
And let him come who would test by experience what we have now said, and in the very presence of the deceit of demons and the imposture of oracles and the marvels of magic, let him use the Sign of that Cross which is laughed at among them, and he shall see how by its means demons fly, oracles cease, all magic and witchcraft is brought to nought. [NPNF 2-04: 62, On the Incarnation of the Word, ch. 48]
And whereas formerly demons used to deceive men’s fancy, occupying springs or rivers, trees or stones, and thus imposed upon the simple by their juggleries; now, after the divine visitation of the Word, their deception has ceased. For by the Sign of the Cross, though a man but use it, he drives out their deceits. [NPNF 2-04: 62, On the Incarnation of the Word, ch. 47]
[W]hereas by the sign of the Cross all magic is stopped, and all witchcraft brought to nought, and all the idols are being deserted and left, and every unruly pleasure is checked, and every one is looking up from earth to heaven: Whom is one to pronounce dead? Christ, that is doing so many works? But to work is not proper to one dead. [NPNF 2-04: 53, On the Incarnation of the Word, ch. 41]
For me, the possibility that this great saint, who so ably formulated almost singlehandedly the doctrine of the Incarnation, is reason enough to employ this ancient sign in faith.
St. Cyril of Jerusalem speaks to this subject in his Catechetical Lectures.
If any disbelieve the power of the Crucified, let him ask the devils; if any believe not words, let him believe what he sees. Many have been crucified throughout the world, but by none of these are the devils scared; but when they see even the Sign of the Cross of Christ, who was crucified for us, they shudder. [NPNF 2-07:82, lecture XIII]
St. Basil’s powerful tome On the Holy Spirit contains the following:
Or were we to attempt to reject such customs as have no written authority, on the ground that the importance they possess is small, we should unintentionally injure the Gospel in its very vitals; or, rather, should make our public definition a mere phrase and nothing more. For instance, to take the first and most general example, who is thence who has taught us in writing to sign with the sign of the cross those who have trusted in the name of our Lord Jesus Christ? [NPNF 2-08: 41, ch. XXVII]
This is also a compelling witness in behalf of the unwritten tradition of the church as being authoritative in the minds of the early Christians. One hopes that people who have rejected the sign of the Cross have not, as St. Basil says, “unintentionally injured the Gospel in its very vitals.”
While the Protestant attack on this as a mindless, powerless and even superstitious repetition has some validity if the sign is done thoughtlessly and without faith, that in no way invalidates the practice itself. If so, then we would also have to toss out prayer or singing of hymns which can also be done without any thinking. The fact is, if this is done reverently, it is not vain or useless. It is a humble way to remind oneself of the death of Christ and to “bear the cross” every day. How can anyone honestly stand against that? And if the Early Fathers are correct (as I believe) then we are depriving ourselves of a powerful weapon if we neglect the sign of the cross.
