Crossing oneself was practiced by Christians from the earliest centuries and may go back to apostolic times. We know that is was already a common ceremony used daily in A.D. 200, for Tertullian writes: "In all undertakings -- when we enter a place or leave it; before we dress; before we bathe; when we take our meals; when we light the lamps in the evening; before we retire at night; when we sit down to read; before each task -- we trace the sign of the cross on our foreheads." St. Augustine (A.D. 431) speaks of this custom many times in his sermons and letters.
It is one of the traditional ceremonies that was most definitely retained by Luther and the Lutheran Church in the 16th-century Reformation. Luther prescribed in his Small Catechism under the heading: "How the Head of the Family Should Teach His Household to Bless Themselves in the Morning and in the Evening." He says, "In the morning when you rise (In the evening when you go to bed) you shall bless yourself with the sign of the holy cross and say: In the name of God the Father, Son, and Holy Ghost. Amen." Again in his Large Catechism he recommends that parents should instruct their children to cross themselves for the purpose of recalling their divine Protector in moments of danger, terror, and temptation. This ceremony is also still authorized in many present-day Lutheran service books.
Crossing oneself is done by puting the fingers of the right hand to the forehead, to the breast, and to the left and right shoulders, with the words, "In the name of the Father and of the Son and of the Holy Ghost. Amen." By doing this we profess our faith in the Triune God and in our redemption through Christ crucified. But it is more than a profession of faith; it is a prayer in action of thanksgiving or for blessing to God the Father, in the Holy Spirit, through our one and only Mediator, Jesus Christ. The sign of the cross may also be made from the right to the left shoulder. This is the older form, which has been retained in the Eastern church.
In the church's worship it is a laudable custom to cross ourselves at the beginning and end of all services and at the following places in the Service or in the Order of the Holy Communion Service: During the opening words, "In the name etc."; at the end of the Absolution; at the beginning of the Introit; at the end of the Gloria in Excelsis; when the Gospel is announced (At this point the sign is made with the hand closed, using the tip of the thumb, upon the forehead, lips, and breast.); at the end of the creed; during the Sanctus at the words, "Blessed is He"; after the consecration at "The peace of the Lord"; when we receive the holy body and precious blood of Christ; when the minister says, "Depart in peace"; and at the end of the Benediction.
The holy cross is the symbol of our salvation. We were signed with it when we were baptized. It is the sign by which the church blesses people and things. By it we become part of the wonderful history of our faith and companions in the company of the saints. It is right that we should make the sign of the cross frequently and to glory in it, saying with St. Paul, "God forbid that I should glory save in the cross of our Lord Jesus Christ." (Gal. 6:14)
(Paul H. D. Lang, Ceremony and Celebration, Concordia Publishing House, St. Louis, MO, 1965)
Among all the ancient writers there is indeed frequent mention of the sign of the cross. ...at the time of Tertullian and afterward the Christians with their fingers formed a transverse figure like a cross in the air, and in this way identified themselves. It was...a profession and reminder that they believed in Christ crucified, and that they were placing all their hope and confidence in Him. (Martin Chemnitz, Examination of the Council of Trent, Part IV [Saint Louis: Concordia Publishing House, 1986], p. 94)
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