The Use of the Sign of the Cross: This sign is prescribed in our rituals to be frequently used, particularly in the administration of Baptism and in the Sacrifice of the Altar, the Mass; to signify, that all grace is derived from the Passion of Christ. The Cross, furthermore, is marked on various parts of the dress of our ministers, and on the vessels appropriated to the divine service, to denote their destination.
On the altar is raised a cross with the figure of our crucified Saviour placed upon it, to bring to our minds that it was He who died for the sins of the world, and that there is no other name under Heaven whereby we must be saved. Finally, we often sign ourselves with the sign of the cross, pronouncing at the same time the words,
"In the name of the Father, and of the Son and of the [Holy Ghost or Holy Spirit]",
thereby attesting our belief in the blessed Trinity, and in the incarnation and death of our Saviour. Jesus Christ.
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The Use of Holy Water in the Church: From the history of the earliest ages of the Church we learn that it was the practice to bless all inanimate things destined for the use of man, and particularly such as were used in the service of religion. Thus, a blessing was pronounced over the water and oil used in the administration of the sacraments. Besides this, water, mixed with salt that had been blessed, was placed at the porch of churches, with which the faithful washed their hands and signed their foreheads as they entered; and with the same water they, and other things, were often sprinkled by the minister.
Salt, mingled with the water, is deemed the emblem of prudence and incorruption; and the water denotes purity and innocence of heart. When the parishioner enters their Catholic parish, and applies Holy Water, with the sign of the cross, to his forehead, he is admonished, by the action, of the cleanliness of heart and hand he should have in the presence of his Maker.
The Church's Scriptures that support the Sign of the Cross and Holy Water.
The importance of the Word of the Cross
18 The word of the cross to them indeed that perish is foolishness; but to them that are saved, that is, to us, it is the power of God.
1 Corinthians 1:18
The importance of preaching Christ crucified
23 We preach Christ crucified, unto the Jews indeed a stumbling-block, and unto the Gentiles foolishness; 24 but unto them that are called, both Jews and Greeks, Christ the power of God and the wisdom of God.
1 Corinthians 1:23-24
The importance of preaching Christ crucified
2 For I judged not myself to know anything among you, but Jesus Christ, and Him crucified.
1 Corinthians 2:2
The importance of the Cross of Christ to St. Paul
14 But God forbid that I should glory, save in the cross of our Lord Jesus Christ; by whom the world is crucified to me, and I to the world.
Galatians 6:14
Paul encourages the Philippians to be obedient unto death, even to the death of the cross
8 He humbled Himself, becoming obedient unto death, even to the death of the cross. 9 For which cause God also hath exalted Him, and hath given Him a name which is above all names; 10 that in the name of Jesus every knee should bow, of those that are in Heaven, on earth, and under the earth."
Philippians 2:8-10