Matthew 5:33–37 (ESV)
you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’34 But I say to you, Do not take an oath at all, either by heaven,
for it is the throne of God,35 or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King.36 And do not take an oath
by your head, for you cannot make one hair white or black.37 Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.
Jesus tells His disciples not to take an oath at all, expressing a general rule of conduct for them. The bottom line for Jesus is truthfulness.
When believers lie or exaggerate commitment, they are not letting their light shine. This rule applies especially when believers converse with fellow Christians. However, there may be times when Christians will be asked to take an oath in their earthly affairs
or contacts with governing authorities. Out of loving consideration for this request, Christians may comply. Thanks be to God that He vowed to save us (cf Ti 1:2) and fulfilled that vow by His Son’s life, death, and resurrection for our salvation.
I pray: Lord Jesus, help me speak the truth in all my conversations and testimony. Amen.
Engelbrecht, E. A. (2009). The Lutheran Study Bible (p. 1588). St. Louis, MO: Concordia Publishing