31. And sware one to another. Isaac does not hesitate to swear; partly, that the Philistines may be the more easily appeased; partly, that he may not be suspected by them. And this is the legitimate method of swearing, when men mutually bind themselves to the cultivation of peace. A simple promise, indeed, ought to have sufficed; but since dissimulations or inconstancy causes men to be distrustful of each other, the Lord grants them the use of his name, that this more holy confirmation may be added to our covenants; and he does not only permit, he even commands us to swear as often as necessity requires it. (Deuteronomy 6:13.) Meanwhile we must beware, lest his name be profaned by rashly swearing.