Jesus teaches people about promises to God
33 ‘You also know the rule that God gave to your ancestors: “If you make a promise to God, you must do what you have said.” 34 But what I tell you is this. Do not use any name to make a promise stronger. Do not use the words “by heaven” to make a promise stronger. Heaven is the place where God rules. Do not use the words “by the earth” to make a promise stronger. The earth is the place where God rests his feet. 35 Do not use the words “by Jerusalem” to make a promise stronger. Jerusalem is God's city. He is the great King who rules from there. 36 Do not use the words “by my head” to make a promise. You cannot make the colour of even one of your hairs black or white. 37 Instead, when you make a promise, you should say only “Yes, I will do it.” Or you should say only “No, I will not do it.” If you say anything more than this, what you say is bad. It comes from Satan.’
5:37People used to say these extra words when they made a promise. They wanted other people to know that they would keep their promise. Jesus taught that we should always keep our promises (do what we promised to do).