An “oath” is a solemn declaration (based on an appeal to God or to some revered object) that one will speak the truth (or keep a promise). The Bible speaks about the oath in a number of places. James 5:12 is a kind of summary statement: “But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath; but let your yea be yea, and your nay, nay, lest ye fall into condemnation.”
Generally we think of two kinds of oaths. There are “common” oaths and there are “civil” oaths:
Common oaths — Sometimes a person in private conversation, says, “I’ll swear to it.” Children playing at school will say, “Cross my heart and hope to die, if I’m not telling the truth.” These are attempts to guarantee the truth of what is being said by appealing to some revered object.
The common oath also includes profane swearing and the use of euphemisms. Swearing is calling upon the name of God to express feelings of anger, and resentment, and over-emphasis. Euphemisms are mild words substituted for outright profanity. Both are flippant uses of God’s name to guarantee the strength or truth of one’s statements.
Civil oaths — One called upon as a witness in court, is asked to place his hand on a Bible, and to solemnly swear to tell the truth. In the courts, it is a very serious matter to promise (in God’s name) to tell the truth, and then tell a lie. The crime is known as perjury.”
One who “swears” before a court of justice implies that he doesn’t always tell the truth, but now that he has placed his hand on the Bible and said “I do solemnly swear,” he is promising to be truthful in what he says. The Bible, however, says that a Christian is to be clearly identified with truth telling at all times. His “yes” means “yes.” His “no” means “no.” He doesn’t need an oath to guarantee that what he says is true. The Christian is to be so careful with his speech at all times, that it will be said of him as it was commonly said of the early Brethren – “Their word is their bond” – or, “Their yes is equal to the world’s oath.”
The laws of our land recognize the convictions of those who cannot swear an oath in good conscience, and the law permits us to simply “affirm” instead. When we “affirm” that what we are about to say is true, we simply state that we mean to tell the truth as far as we understand it. Our experience has shown that the judge usually welcomes testimony from those who say they cannot in good conscience swear over a Bible, but who affirm to tell the truth.