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.
When you make a vow to God, do not delay to pay it; For He has no pleasure in fools. Pay what you have vowed— Better not to vow than to vow and not pay. Eccl. 5:4-5 NKJV
If a man makes a vow to the Lord , or swears an oath to bind himself by some agreement, he shall not break his word; he shall do according to all that proceeds out of his mouth. Num. 30:2 NKJV
Speak to the children of Israel, and say to them: ‘When either a man or woman consecrates an offering to take the vow of a Nazirite, to separate himself to the Lord,
Num. 6:2 NKJV
6:2 The Nazirite was either a man or woman who dedicated himself or herself fully to God for a stated period of time. Parents could dedicate their children as Nazirites for their whole life. This was done in the case of Samson, the only person in the Bible mentioned by name as being a Nazirite (Judges 13:5). It is possible that Samuel was one, judging from his mother’s vow in 1 Sam 1:11. Certainly he was dedicated to the Lord for life (1 Sam 1:27-28). There were other Nazirites too but we are not told any of their names (Amos 2:11-12). It is said of John the Baptist that he would drink no wine (Luke 1:15), possibly indicating that he was to be a Nazirite. In this Church age all believers are to fully dedicate themselves to God (Rom. 12:1-2), they are to be spiritual Nazirites – which has nothing to do with not eating grapes or having long hair.
Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform your oaths to the Lord.’ But I say to you, do not swear at all: neither by heaven, for it is God’s throne; nor by the earth, for it is His footstool; nor by Jerusalem, for it is the city of the great King. Nor shall you swear by your head, because you cannot make one hair white or black. But let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No.’ For whatever is more than these is from the evil one. Matt. 5:33-37 NKJV
5:33-37 “Swear”– refers to the voluntary (and often very careless) use of oaths in every day life to convince others that one is telling the truth. Jesus tells us to be men of our word, absolutely truthful in all we say and promise. As Jesus’ disciples we must never say yes when we mean no, or say no when we mean yes. Lying and deception are hateful to God and have no place in God’s kingdom. And as God’s children we should never take God’s name in vain or use it lightly, but show proper reverence for His name and all that pertains to Him (Ex 20:7).
The principle here is clear for Christians: be careful about making vows, either to the Lord or to one another. Further, the informal vows we make (“I swear by all the angels in heaven!”) are completely unnecessary. Our word is our bond.