The Old Testament forbade bearing false witness, including making an oath and not fulfilling it. Jesus encouraged not to swear fake oaths, but to just say yes or no. Swearing by external things is artificial and does not guarantee fulfillment of an obligation. Using this form of leverage supposedly makes a person more believable. It emphasizes how we humans are too often unreliable and untruthful. By invoking heaven or earth, we delude ourselves that this veneer of honesty can change liars into truth-tellers and covenant breakers into contract keepers. We Christians do not need to engage in such self-deceptive swearing. We simply need to be truthful as best as we can.