Matthew, chapter 5, verse 37: "Let your 'Yes' be 'Yes,' and your 'No,' 'No.' Anything more comes from the evil one."
This verse is part of Jesus' Sermon on the Mount, a section of the Gospel of Matthew where Jesus provides a series of moral teachings.
In the larger context, this verse is a part of Jesus' discussion about oaths. In the preceding verses, Jesus instructs his followers not to swear oaths at all, neither by heaven, for it is God's throne; nor by earth, for it is his footstool; nor by Jerusalem, for it is the city of the Great King; nor by their head, for they cannot make a single hair white or black. Instead, he tells them to let their "yes" mean "yes," and their "no" mean "no."
Jesus pointed out that truthfulness should not be exceptional, guaranteed by an oath, but a simple, straightforward characteristic of all communications. He was teaching that it is better always to speak the truth to avoid invoking commitments. A simple "yes" or "no" will suffice for an answer if someone is always truthful. Anything more than a simple affirmation or denial tends to lead to unnecessary complications, falsehood, or deception, which Jesus attributes to the "evil one."
This concept has been influential in Christian ethics, with many interpreting it as a commandment against lying or deceiving. Instead, it calls for integrity, honesty, and simplicity in speech and actions. This applies to speaking and all forms of communication, including our actions and behaviors.
This principle is also echoed in the book of James (James 5:12): "Above all, my brothers and sisters, do not swear--not by heaven or by earth or anything else. You only need to say a simple 'Yes' or 'No.' Otherwise, you will be condemned." The apostle James' teaching aligns with that of Jesus, reaffirming the importance of honest communication in the Christian life.