A little context is needed here to better understand why Jesus is saying this. For the jewish people oaths were taken only for the purpose of covenants. An oath would call down God’s participation into the covenantal union being established. Meaning, those that fulfilled the oath would be blessed by God and those that broke the oath would be cursed by God. An oath required, faith and love and commitment, and it was understood that it was not to be taken lightly.
Jesus here reminds of this fact, invoking the law and saying “Do not take a false oath, but make good to the Lord all that you vow.” This comes from the Law given to Moses on the mountain, directly from God. An oath if made can only be made in the name of God, anything else will not be recognized. But many jews of this time were out making oaths in the name of heaven, or the earth, or Jerusalem, or even on their own heads. These oaths were fraught with error and deceit. They were erroneous, because they were not valid, and not recognized by divine law, and they were deceitful, because they appeared on the outside to have authority, and power behind, them but they were actually just empty hollow promises. This practice essentially allowed people to claim that they would do something, with no assurance that there would be any follow through.
There was great temptation in using this practice. You could gain power and authority, without any consequences for not keeping your oath. St. Cornelius of Lapide said that the temptation could either come from the devil directly trying to tempt you into perjuring yourself, or maybe even personal vice, or irreverence toward Gods law and his commandments. In either case being and oath-breaker was punishable by death, and so by making an oath in the name of heaven, or earth, or even your own head, would not hold you to that same standard and consequence.
But Jesus in today’s reading says “Let your ‘Yes’ mean ‘Yes,’ and your ‘No’ mean ‘No. Anything more is from the Evil One.” Because He hates lies and deceit, and He wants you to not allow yourself to fall for these temptations, and instead be upright, and truthful, and keep your word whether it is a simple promise or a covenantal oath. Anything short of that is a demonic lie.
I believe that this message is one that speaks directly into our time today. The devil has succeeded in separating so many of God’s people from Him, and His divine will. We have vast numbers of people that have stopped looking to God for answers to what is right and wrong, and have instead decided to look inside themselves for the truth. They tell us that “you have your truth, and I have my truth,” and “you do you.” The whole world has it all backwards. There is only one truth and it is God, and you can only swear an oath or make promise by one name, and that is Jesus. Anything that is less than that is a lie from the devil.
