The complete drawing of the cross (The Great Bible) is: with the number of the cross (draw the first small cross on the forehead), God waits for our Lord (draw the second small cross on the mouth), and saving me is equal to revenge (draw the third small cross on the chest), because of the father, the factor, and the name of the Holy Spirit (draw the big cross), and amen (put your hands together).
The church calls the cross a sacred symbol, so it is called a "holy book" because it is necessary to draw a cross when reading these two verses. When we draw a cross, we put our left hand on our chest, which means we believe that the Lord is in my heart.