The Importance Of The Sign Of The Cross
The Sign of the Cross is the chief sacramental used by the Church. We make the Sign of the Cross by putting the right hand to the forehead, then on the breast, and then to the left and right shoulder, saying: "In the name of the Father, and of the Son, and of the Holy Spirit." Amen.
A common fault with many people blessing themselves is to make a hurried gesture, a bit like swatting flies with the right hand, which is in no way a Sign of the Cross. They perform this devotion without any thought or intention, forgetting that the Church grants an indulgence to all who bless themselves properly while they have sorrow for their sins.
We make the Sign of the Cross to show the we are Christians and to profess our belief in the main mysteries of our faith. The Sign of the Cross is a profession of faith in the main mysteries of our religion because it expresses the mystery of the Unity and Trinity of God and the Incarnation and death of Jesus Christ.
The words: "In the name of the Father, and of the Son, and of the Holy Spirit," expresses the mystery of the Trinity and also of the Incarnation by reminding us that the Son of God, having become man, suffered death on the Cross.
St Basil (379) tells us that the practice of using the Sign of the Cross was introduced by the Apostles.
Tertullian wrote in the 2nd century: "Whenever we come in or go out, when we put on our sandals or wash or eat our meals.......whether we are about to recline or sit down.........
we impress on our forehead the Sign of the Cross."
St. Jerome in the fourth century writes to a Roman lady, Eustochia: "Before every action, at every step, let your hand form the Sign of the Cross.
This should be sufficient to convince us that in using the Sign of the Cross we are associating ourselves with the greatest and holiest of the followers of Christ in the first centuries of Christianity. It is, in fact, an act of Faith and a prayer by which we offer to God what we are about to do.
The Sign of the Cross can also be offered in reparation for the blasphemies committed against the Sacred Heart of Jesus and the Immaculate Heart of Mary, for the conversion of sinners, etc.
"Amen" means, "truly" or "it is true," and expresses acceptance of what has just been said. It is an act of confidence that the Father is moved by this "Amen," which Jesus so often used to stress the divine authority of His words.
Source: Commentary on the Catechism.