What does Matthew 5:37 mean?

Once again, Jesus is countering the shallow interpretation of Old Testament law, coming from Israel's religious leaders. In this passage, He has criticized the use of oaths: in this context, meaning the type of casual, "I swear I will do this" promises made in conversation. In Christ's era, people might have sworn oaths on "heaven and earth," or their own life, rather than swearing to the Lord, to avoid the consequences of breaking such a promise (Numbers 30:2). Jesus has already dismissed that practice (Matthew 5:33–36). Since all things belong to the Lord, nobody should take an oath on any of them.

Here, Jesus explicitly explains why using oaths to "enhance" a promise is not only unwise, it's sinful. When someone declares a promise with an oath, they're undermining their own personal integrity and honesty. The oath implies, "I really, truly mean what I am saying," which suggests other, non-oath-bound statements might not be so sincere. There's a built-in suggestion that the oath-swearer has a varied commitment to honesty. It's also a form of manipulation, seeking to get agreement from the other person using dramatic terms.

Christ's command for believers is simple: let the words "yes" and "no" be binding in all cases. Anything more comes from evil. A believer ought to be honest in what they say and do—they should not need the pressure of an artificial oath to follow through on their commitments. And, the believer should live a life of integrity such that others trust them without seeking such oaths. Modern culture echoes that with phrases such as "that man's word is his bond." This is the ideal: if you say you will do it, you will, period. No oaths required.

What Jesus does not refer to here are "oaths" such as contracts, marriage vows, or swearing in a witness in a courtroom. He is not forbidding believers to make promises, but to use oaths as an artificial form of honesty.