The Sign of the Cross is one of the precious sacramentals abandoned by many of the Protestant reformers and one of the great and powerful treasures of the Catholic faith. Because of this, many Protestants do not understand why we Catholics value this simply but profound gesture and we need to have a ready explanation, both accurate and personal.
Thomas Howard has written that the Sign of the Cross "is a formula not to be spoken lightly." He is very right in this because, as Roman Guardini observed, the Sign of the Cross is "the holiest of all signs." (For citations, see this homily.)
In a previous post, I explained why we make the Sign of the Cross from left to right.
This ancient sign has been used by the followers of Jesus Christ earlier than the first recorded instance of it that we have from Tertullian in the year 211:
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 occupy us, we [Christians] mark our foreheads with the sign [of the cross]."On a related note, many Protestants do not agree with the ancient use of crucifixes, of crosses with the image of the Crucified Lord, even though they are very Biblical in nature. Saint Paul wrote that "we proclaim Christ crucified" (I Corinthians 1:23) and that he "resolved to nothing while I was with you but Jesus Christ, and him crucified" (I Corinthians 2:2).