Let what you say be simply ‘Yes’ or ‘No'; anything more than this comes from evil.
The golfer Bobby Jones was a man of scrupulous honesty. Once, somebody complimented him for leaving his ball in a sand trap even though he’d had an opportunity to take it out before anybody noticed it was there. Jones was mightily offended saying, “You may as well compliment me for not robbing a bank.” Jones had a lively awareness that honesty was something more than “Be careful only to lie when people are not going to catch you.” In this, he showed himself to be in touch with the spirit of today’s verse. For Jesus also assumes that his disciples should simply speak the truth and not have to buttress themselves with a bunch of appeals to God, as though there is “truth” and “truthplus”. If we are not honest, calling God as our witness will only have the effect of making him a witness to our dishonesty, and that is to take his name in vain. Today, make your speech plain and truthful and don’t bother to embroider it with unnecessary oaths.