I'll be honest. There are some topics the New Testament talks about that bore me and oath-taking is one of them. That and fasting. I guess I'm a product of my culture. In our culture taking oaths is something you only see done as a formality and you're never sure if it means anything to anyone. Couples take oaths on their wedding day then divorce a few years later. Witnesses take oaths in court then lie on the stand. So when Jesus says, "Make no oath at all either by heaven or earth" I just think, "Well, good. I guess that takes care of that" and I move on, glad to be rid of the subject.
If you dig deeper, however, there is something interesting about this passage and the context in which Jesus delivers this teaching. Apparently back then the rabbis accepted the practice of taking non-binding oaths. If you avoid swearing by God's name and instead substitute some lesser object such as "heaven" or "earth" or "Jerusalem" or "your head," it would be perfectly okay to break the oath later on. See, it's because you didn't swear by the name of Yahweh. You didn't take the real McCoy, one hundred percent, purely authentic oath. You only took the low-calorie, sugar-free, Jenny Craig version.
Jesus is having none of this casuistry. Saying you technically didn't swear by God's name doesn't get you off the hook. Because if you swear by heaven it is God's throne; if you swear by earth it is his footstool; if you swear by Jerusalem it is his city; and if you swear by your head it is his creation. Don't think you can make an oath with a loophole so you can wiggle through it later on. God isn't taken in by your foolish little word tricks. Say "yes" if you mean yes and "no" if you mean no. Anything else is evil.
"Anything else is evil." This once boring passage has officially gotten interesting. God has no patience for people who manipulate words to serve their own purposes. Fancy lawyer arguments, verbal sleights of hand, equivocation, euphemisms. All the court cases where the guilty party gets off on a technicality. All the times when an abuser convinces the victim that he or she deserved the abuse. All the times history is rewritten to serve some other purpose than the truth. Anything other than what is honest, forthright and true, says Jesus, is evil.