Why do we make the sign of the cross, and why from right to left?

The Orthodox nuance

First, why with the body. Man is not just a spirit; he is body and soul together, so he prays with all that he is. When you make the sign of the cross, you preach without words. The three joined fingers—thumb, index, and middle—profess the Trinity, one God in three Persons. The other two fingers tucked into the palm profess the two natures of Christ, divine and human. The entire Creed, in one hand.

Then the movement. You touch the forehead, then the chest, then the right shoulder, then the left. From top to bottom, because God descended to us. From right to left, because the right side is, in Scripture, the place of honor, the place of the saved, and Christ places the blessed on His right (Matthew 25:33). Westerners do it the opposite way, from left to right; it is a difference of custom, not of faith, but for us the gesture carries precisely this meaning.

And it is not a formality to check off. The Fathers said that the sign of the cross drives away fear and puts temptations to flight, not like magic, but because through it you attach yourself to Christ's victory over death. That is why we cross ourselves to pray, entering the church, before a meal, when going through a trial. It is as if you place the Master's seal on everything you do.