The second commandment
forbids false oaths.
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.”
Rejection 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 hu
man speech with God’s truth. A false oath calls on God to be
witness to a lie.
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.
In 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 ei
ther witness to or mock.
Following St. Paul,
the tradition of the Church has un
derstood Jesus’ words as not excluding oaths made for grave and
right reasons (for example, in court). “An oath, that is the invoca
tion of the divine name as a witness to truth, cannot be taken un
less in truth, in judgment, and in justice.”
5:33-34, 37; cf.
84 CIC, can. 1199 § 1.