Since lies are a continual reality in our world, it is no surprise that every society has developed a system of contracts and oaths to try and deal with the problem. An offer to purchase for a house, a marriage contract, indemnity forms, bank statements, and proof of income—we need truth for relationships to work. Especially where someone’s word can put another person in jail or bring about their death, truth matters.

In ancient times, people were encouraged to swear an oath to their god in order to affirm the truthfulness of a statement. In a court of law where there was no hard evidence and a matter was decided based on the statements of one or two witnesses, you would swear to your god with the understanding that he will strike you dead if your words are not true. If you refused to take an oath, it was assumed that you were guilty.

This expectation and language naturally moved from the court into the marketplace, so that it became common practice for people to swear in order to affirm the truth of their words. A modern example of the same is the phrase: Cross my heart hope to die stick a needle in my eye.

Coming to the people of Israel, things were no different. We read in Deuteronomy 10:1–22 that God tells his people to swear in his name. He is the Lord who has rescued them from Egypt. They belong to him; they must call him to bear witness to the truth of their words. There was nothing wrong per se with an oath. The problem came when God’s people sought to establish a system to determine when oaths were binding and when they were not. Because it is in our nature to lie, plans were made for small print, for a lie to be cleverly hidden and excused, while at the same time claiming obedience to God’s commandments. Just like we had with murder and adultery, sinful people naturally limit God’s law to excuse our sin.

The way it worked in Israel was as follows: We know the ninth commandment specifically concerns a court of law; we are not allowed to give false testimony in such a place. Likewise, we know that third commandment says we must not misuse God’s name. We cannot swear an oath to the Lord, or in his name, and then fail to carry it out. That much is clear, we are all in agreement. But what if we were to swear by something that stands as a proxy of God? You see, Numbers 30:1–16 says that it is only oaths sworn in the Lord’s name that must be kept. If your vow was not vowed to the Lord and directly connected with his name, surely then you have freedom to leave it if circumstances change?

The key, then, became to swear by something that indirectly connects with God, so that you can convince someone you will keep your word while at the same time giving yourself leeway to ignore your vow with a clear conscience. The result was a complex system with all sorts of qualifications (see Matthew 23:16–22). Swear by the temple and there is room to manoeuvre. Swear by the gold of the temple, then you are stuck and you must do what you said. Swear by the altar and it is nothing. Swear by the gift of the altar and it is a different matter.

This is the system that Jesus is challenging and correcting. He is not forbidding any and all vows. He is not drawing a line through what God had previously revealed, as if vows were for the old covenant and not for the new. If you read through Paul’s letters to the Romans and Thessalonians, you will see that he calls on God to be his witness. He is not averse to oaths when they serve God’s purposes.

Hebrews 6:1–20 also affirms that oaths can be legitimate. God himself swears an oath when it serves to encourage us to that we take his words seriously. In fact, we can even consider the sacraments to be an oath of sorts. A promise from God to affirm invisible spiritual realities. The breaking of bread, the drinking of wine—these are visual testimonies to the work that Christ has done for us if we believe.

This caveat is important because there are some Christian groups who think that all oaths and vows are sinful. That is a misunderstanding of what Jesus says. He is taking God’s people back to the root of the matter. Murder begins in the heart. Adultery begins with lustful thoughts. And behind all vows and oaths is God’s concern for truth. They are meant to serve truth, not to undermine it. They are meant to limit small print and second guessing and not to be the source of the same.

God is truth. In him there is no evil. He does not lie and neither must his people. Where oaths are used to excuse falsehood, they must be done away with. After all, it does not matter if you swear by heaven, Jerusalem, or your head, God sees everything. He knows everything and his name is invoked in every vow.

Instead of finding excuses to break your word, instead of saying that you did not promise, you did not swear, instead of these extra words and systems, simply let your yes be yes and your no, no. Be a people who are known for speaking the truth and keeping commitments. Be a people who emulate God by saying what you mean and meaning what you say.