Có nhiều cách giải thích, theo các Cha đạo thì:
Trán-Nước Trời.
Bụng-Đất.
Vai-Sức mạnh.

Motion
The sign of the Cross is made by touching the hand sequentially to the forehead, lower chest or navel area, and both shoulders, accompanied by the Trinitarian formula: at the forehead In the name of the Father (or In nomine Patris in Latin); at the stomach or heart and of the Son (et Filii); across the shoulders and of the Holy Spirit/Ghost (et Spiritus Sancti); and finally: Amen.

There are several interpretations, according to Church Fathers:[1] the forehead
symbolizes Heaven; the stomach, the earth; the shoulders, the place and sign of power.

http://en.wikipedia.org/wiki/Sign_of_the_Cross

Amen=So be it: nguyện xin được như thế.
The word amen ( /ˌɑːˈmɛn/ or /ˌeɪˈmɛn/; Hebrew: אָמֵן, Modern amen Tiberian ʾāmēn; Greek: ἀμήν; Arabic: آمين‎, ʾāmīn ; "So be it; truly") is a declaration of affirmation[1][2] found in the Hebrew Bible and New Testament. Its use in Judaism dates back to its earliest texts.[3] It has been generally adopted in Christian worship as a concluding word for prayers and hymns.[2] In Islam, it is the standard ending to Dua (supplication) and the "Opening" chapter of the Qur'an. Common English translations of the word amen include "verily" and "truly". It can also be used colloquially to express strong agreement,[2] as in, for instance, amen to that.[4]

http://en.wikipedia.org/wiki/Amen