Catechism of the Catholic Church: Article 2:The Second Commandment
II. Taking the Name of the Lord in Vain
2150The second commandment forbids false oaths. Taking an oath or swearing is to take God as witness to what one affirms. It is to invoke the divine truthfulness as a pledge of one's own truthfulness. An oath engages the Lord's name. "You shall fear the LORD your God; you shall serve him, and swear by his name."
2151Rejection of false oaths is a duty toward God. As Creator and Lord, God is the norm of all truth. Human speech is either in accord with or in opposition to God who is Truth itself. When it is truthful and legitimate, an oath highlights the relationship of human speech with God's truth. A false oath calls on God to be witness to a lie.
2152A person commits perjury when he makes a promise under oath with no intention of keeping it, or when after promising on oath he does not keep it. Perjury is a grave lack of respect for the Lord of all speech. Pledging oneself by oath to commit an evil deed is contrary to the holiness of the divine name.
2153In the Sermon on the Mount, Jesus explained the second commandment: "You have heard that it was said to the men of old, 'You shall not swear falsely, but shall perform to the Lord what you have sworn.' But I say to you, Do not swear at all. . . . Let what you say be simply 'Yes' or 'No'; anything more than this comes from the evil one." Jesus teaches that every oath involves a reference to God and that God's presence and his truth must be honored in all speech. Discretion in calling upon God is allied with a respectful awareness of his presence, which all our assertions either witness to or mock.
2154Following St. Paul, the tradition of the Church has understood Jesus' words as not excluding oaths made for grave and right reasons (for example, in court). "An oath, that is the invocation of the divine name as a witness to truth, cannot be taken unless in truth, in judgment, and in justice."
2155The holiness of the divine name demands that we neither use it for trivial matters, nor take an oath which on the basis of the circumstances could be interpreted as approval of an authority unjustly requiring it. When an oath is required by illegitimate civil authorities, it may be refused. It must be refused when it is required for purposes contrary to the dignity of persons or to ecclesial communion.
III. The Christian Name
2156The sacrament of Baptism is conferred "in the name of the Father and of the Son and of the Holy Spirit." In Baptism, the Lord's name sanctifies man, and the Christian receives his name in the Church. This can be the name of a saint, that is, of a disciple who has lived a life of exemplary fidelity to the Lord. The patron saint provides a model of charity; we are assured of his intercession. The "baptismal name" can also express a Christian mystery or Christian virtue. "Parents, sponsors, and the pastor are to see that a name is not given which is foreign to Christian sentiment."
2157The Christian begins his day, his prayers, and his activities with the Sign of the Cross: "in the name of the Father and of the Son and of the Holy Spirit. Amen." The baptized person dedicates the day to the glory of God and calls on the Savior's grace which lets him act in the Spirit as a child of the Father. The sign of the cross strengthens us in temptations and difficulties.
2158God calls each one by name. Everyone's name is sacred. The name is the icon of the person. It demands respect as a sign of the dignity of the one who bears it.
2159The name one receives is a name for eternity. In the kingdom, the mysterious and unique character of each person marked with God's name will shine forth in splendor. "To him who conquers . . . I will give a white stone, with a new name written on the stone which no one knows except him who receives it." "Then I looked, and Lo, on Mount Zion stood the Lamb, and with him a hundred and forty-four thousand who had his name and his Father's name written on their foreheads."
In Brief
2160"O Lord, our Lord, how majestic is your name in all the earth" (Ps 8:1)!
2161The second commandment enjoins respect for the Lord's name. The name of the Lord is holy.
2162The second commandment forbids every improper use of God's name. Blasphemy is the use of the name of God, of Jesus Christ, of the Virgin Mary, and of the saints in an offensive way.
2163False oaths call on God to be witness to a lie. Perjury is a grave offence against the Lord who is always faithful to his promises.
2164"Do not swear whether by the Creator, or any creature, except truthfully, of necessity, and with reverence" (St. Ignatius of Loyola, Spiritual Exercises, 38).
2165In Baptism, the Christian receives his name in the Church. Parents, godparents, and the pastor are to see that he be given a Christian name. The patron saint provides a model of charity and the assurance of his prayer.
2166The Christian begins his prayers and activities with the Sign of the Cross: "in the name of the Father and of the Son and of the Holy Spirit. Amen."
2167God calls each one by name (cf. Isa 43:1).
Notes
72 Ex 20:7; Deut 5:11.
73 Mt 5:33-34.
74 Cf. Zech 2:13; Ps 29:2; 96:2; 113:1-2.
75 John Henry Cardinal Newman, Parochial and Plain Sermons V,2 (London: Longmans, Green and Co., 1907) 21-22.
76 Cf. Mt 10:32; 1 Tim 6:12.
77 Cf. 1 Jn 1:10.
78 Jas 2:7.
79 Cf. CIC, can. 1369.
80 St. Augustine, De serm. Dom. in monte 2,5,19:PL 34,1278.
81 Deut 6:13.
82 Mt 5:33-34,37; Cf. Jas 5:12.
83 Cf. 2 Cor 1:23; Gal 1:20.
84 CIC, can. 1199 § 1.
85 Mt 28:19.
86 CIC, Can. 855.
87 Cf. Isa 43:1; Jn 10:3.
88 Rev 2:17.
89 Rev 14:1.