Question: "What does the Bible say about keeping your vows / oaths?"
Answer: There are about 30 biblical references to vows, most of which are from the Old Testament. The books of Leviticus and Numbers have several references to vows in relation to offerings and sacrifices. There were dire consequences for the Israelites who broke vows, especially vows to God.
The story of Jephthah illustrates the foolishness of making vows without understanding the consequences. Before leading the Israelites into battle against the Ammonites, Jephthah—described as a mighty man of valor—made a rash vow that he would give to the Lord whoever first came out of doors to meet him if he returned home as the victor. When the Lord granted him victory, the one who came out to meet him was his daughter. Jephthah remembered his vow and offered her to the Lord (Judges 11:29–40). Whether or not Jephthah should have kept this vow is dealt with in another article. What this account shows is the foolishness of rash vows.
Jesus taught concerning vows, “You have heard that it was said to the people long ago, ‘Do not break your oath, but keep the oaths you have made to the Lord.’ But I tell you, Do not swear at all: either by heaven, for it is God’s throne; or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King. And do not swear by your head, for you cannot make even one hair white or black. Simply let your ‘Yes’ be ‘Yes,’ and your ‘No ,’ ‘No’; anything beyond this comes from the evil one” (Matthew 5:33–37).
A little background information is helpful in understanding Jesus’ words here. The religious leaders of the day advocated keeping a vow if it was a public vow using God’s name; however, if the vow was made in the course of everyday conversation, referencing only “heaven” or “earth” or “Jerusalem,” it was not really binding. People had a loophole. They could lie or exaggerate in their conversations and lend themselves an air of credibility by saying, “I swear by heaven that this is true!” They could not be held to account because they did not specifically swear by God’s name and the vow was private. Jesus countered that idea. If you swear something, it had better be true, He says. In fact, all you need to say is “yes” or “no.” Your word should be good. There’s no need for overwrought expressions to bolster your case.
Psalm 15:4 describes a righteous person as one “who keeps an oath even when it hurts, and does not change their mind.” Jesus’ teaching in Matthew 5 supports this biblical principle. Oaths are binding, even when spoken frivolously or privately as part of everyday conversation. A promise is a promise, and there is no loophole in God’s eyes to allow a person to renege on an oath.
So, Jesus was not condemning all forms of promises, contracts, or agreements. Jesus was speaking of the kind of spontaneous vow made when a person says, “I cross my heart and hope to die” or “I swear on a stack of Bibles” or “I swear on my mother’s life.” Jesus warns against using those types of flippant oaths. His teaching in Matthew 5 is not meant to discourage careful, thought-out promises, such as wedding vows or a legal contract.
The principle here is clear for Christians: be careful about making vows, either to the Lord or to one another. The fact that we are prone to errors in judgment means that we may make vows foolishly or out of immaturity. Further, the informal vows we make (“I swear by all the angels in heaven!”) are completely unnecessary. Our word is our bond.