"Again, you have heard that it was said to those of ancient times, 'You shall not swear falsely, but carry out the vows you have made to the Lord.' But I say to you, Do not swear at all, either by heaven, for it is the throne of God, or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. And do not swear by your head, for you cannot make one hair white or black. Let you word be 'Yes, Yes' or 'No, No'; anything more than this comes from the evil one. (Matthew 5:33-37)
Jesus continues to illustrate kingdom life, turning to the matter of oaths.
Leviticus 19:2 and Numbers 30:2 prohibit swearing falsely, that is purporting to tell the truth while in fact doing otherwise, whether by outright lying or shading the truth. In the time of Jesus, it appears many folk believed oaths came in varying degrees of seriousness. For example, one might say, "Be it on my own head, if what I say is not true" or "As heaven is my witness, this is true." Such oaths were felt to be less binding than an oath sworn in the name of God.
Jesus says that kingdom people will not use such tactics for two reasons. First, anything we might call as witness to our oaths belongs to God. Invoking such things effectively involves God in our oath, and any attempt to act as if God is not involved is futile. Second, kingdom people should not need oaths. Living in the presence of God, they practice integrity. They do not need an oath to strengthen their own commitment to speak truth or keep their word.
A few commentators attempt to restrict the teaching's application to formal settings, such as the courtroom. Like most Christian commentators I think it applies to all arenas of life, but most especially to giving and keeping one's word and speaking truth in ways appropriate to a given setting.
Of course, I cannot help but think of the passage when I listen to partisans "spin" the words of a political candidate. For example, I watched the entire first debate between the presidential candidates. Each explained his particular approach to diplomatic conversations with leaders of rogue states. One used the term "precondition" to describe his own approach; the other chose the term "preparation." Try as I might, after listening to their explanations of their chosen terms, I could discern little difference in the mechanics of each candidates approach (tone and style, perhaps, are different matters).
Immediately after the close of the debate, political pundits of various persuasions began to "spin the discussion." Most attempted to persuade me (and other viewers) that there was a considerable difference between the two candidates on this matter. To put it gently, the commentators had to shade the truth in order to make the attempt. Most of them, no doubt, have Christian or Jewish affiliations. I was struck, yet again, by how hard it is to take control of our tongues and speak with integrity rather than to use words to serve a particular ideology or party affiliation.
Lest I seem to pick only on political operatives, Baptist preachers have a mixed record at best. For example, the New Testament clearly records two approaches to baptism: one follows personal confession of Jesus as Savior and Lord, the other is administered to entire "families" (perhaps including household servants)when the head of a household becomes a Christian. Baptist preachers, for the most part, "spin" their discussion of the matter to make it sound as if the New Testament presents only one option, namely the one we practice. Again, it's awfully hard not to shade the truth to serve one's own position or felt needs.
One more word: Some Christians use this passage to argue that we must have a clear position on all matters or that we can never change our minds. In other words, they believe it wrong to admit to grey areas, or that one does not know the right answer, or to change one's position in light of new evidence. If ever you say "yes" to a position, it ought to remain your position and so the argument goes. Nothing could be farther from the intention of Jesus. His call for radical truthfulness requires we admit when we do not know, recognize the reality of ambiguity, and declare that we have changed our minds when we have done so.