Jesus saw a problem with the casual way in which grand promises were made that had no intention of being kept. He directly addressed the dramatic way that eloquent people would promise many grand things for the purpose of impressing or persuading people. The most dangerous aspect of this was that the oaths were simply foolish talk by foolish people out to be more important than they really were. Jesus in essence is saying, "Don't let this foolishness ever touch you."

So, let your yes be yes and your no be no. Never swear by God as your witness as God is not to be reduced to a co-signer on a flamboyant promise that will never be kept.