What does it mean to swear falsely (Matthew 5:33)?

In His groundbreaking Sermon on the Mount, Jesus taught a radically new way of living and thinking based on kingdom values. His teaching often sharply contrasted with the customary interpretations of Old Testament law. One example has to do with taking oaths and making vows: “Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, Do not take an oath 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 take an oath by your head, for you cannot make one hair white or black. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil” (Matthew 5:33–37, ESV).

To “swear falsely” means to knowingly tell an untruth while making a promise, oath, or vow; or to swear an oath and then not keep it, especially when invoking God as a witness to your words. Swearing falsely is equivalent to committing perjury or lying under oath. In biblical times, people would often swear oaths to attest to their truthfulness or to demonstrate their commitment to a particular action.

The Old Testament law warned against making false oaths: “A man who makes a vow to the Lord or makes a pledge under oath must never break it. He must do exactly what he said he would do” (Numbers 30:2, NLT; see also Leviticus 19:12; Deuteronomy 23:23). By Jesus’ day, the Pharisees had grossly stretched and obscured this command against swearing falsely, creating a system of legal loopholes that allowed them to evade God’s requirement to speak the truth. Rather than using God’s holy name, they would swear by heaven, earth, Jerusalem, or some part of their body. Jesus overturned this dishonest mentality in Matthew 5:33–37, urging His followers not merely to avoid swearing falsely, but to be so honest that oaths become unnecessary. He insisted that a straightforward “yes” or “no” should be trustworthy and sufficient.

James echoes Christ’s teaching: “Above all, my brothers and sisters, do not swear—not by heaven or by earth or by anything else. All you need to say is a simple ‘Yes’ or ‘No.’ Otherwise you will be condemned” (James 5:12).

Warren Wiersbe writes, “Jesus taught that our conversation should be so honest, and our character so true, that we would not need ‘crutches’ to get people to believe us. Words depend on character, and oaths cannot compensate for a poor character” (The Bible Exposition Commentary, vol. 1, Victor Books, 1996, p. 24).

The Bible emphasizes integrity and truthfulness in all speech (see Zechariah 8:16; Psalm 15:1–5; Proverbs 12:22; 23:23; 1 Timothy 1:10). Paul writes, “Do not lie to each other” (Colossians 3:9) and “speak truthfully to your neighbor” (Ephesians 4:25).

God takes pleasure in truth and honesty, which are marks of an upright character, and He expects His children to reflect these qualities. Jesus calls us to a higher standard: honesty in every word and action, so that there is no need to make elaborate promises or oaths.

Today, “swearing falsely” still refers to lying under oath, breaking promises, or making insincere commitments, whether in a legal, personal, or spiritual context. The principle Jesus taught in His Sermon on the Mount stands today: Christ’s followers are to be people of their word, with integrity and truthfulness guiding all their communication.