Sarah K, a Premium Member student at the New Saint Thomas Institute recently asked:

What is the history of the Sign of the Cross? How can I defend this practice to Protestants/atheists/other religions?

Many of our students responded with excellent answers (if you’re a student of NSTI, you can read them here), but here is my advice to Sarah:

Sarah,

When talking about this with a non-Catholic, you should be succinct and convincing. Protestants prefer “Scripture alone” but they can be swayed by quotes from the earliest Church Fathers. So I would recommend this line of argument:

The Apostles would place the sign of the cross on the foreheads of newly baptized people in fulfillment prophetic visions found in Ezekiel and Revelation. After baptism, Christians would continue to make the sign of the cross on their foreheads, and we see evidence of it in the Bible and Church Fathers. When Christianity became legal, the larger sign of the cross made from head to stomach became adopted. But the original form is simply made with the thumb on the forehead.

SCRIPTURE
Ezekiel speaks of the “mark of the t” administered by the heavenly “man in linen” on the head of the faithful. “Go through the city, through Jerusalem, and put a mark upon the foreheads of the men who sigh and groan over all the abominations that are committed in it.”

The heavenly “man in linen” is the Second Person of the Trinity. Revelation depicts Jesus Christ as the man in linen.

So Ezekiel describes Christ placing a saving “t” or “x” shaped letter on the forehead. The Book of Revelation carries on the description of placing the cross on the forehead.

For my in depth discussion on the sign of the cross as “the mark of the Christ” in the Book of Revelation (in contrast with “the Mark of the Beast:), you can listen for free here.

CHURCH FATHERS
For Church Fathers goes with Tertullian. Writing in around A.D. 204, Tertullian explained that Christians mark their foreheads with the sign of the cross.

In all our travels and movements in all our coming in and going out, in putting of our shoes, at the bath, at the table, in lighting our candles, in lying down, in sitting down, whatever employment occupieth us, we mark our foreheads with the sign of the cross. (Tertullian, De corona milites, 3)

My bestselling novel Sword and Serpent features early Christians often making the signum crucis on their foreheads. You can read a sample and reviews by clicking here at amazon.com.