33 Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform your oaths to the Lord.’ 34 But I say to you, do not swear at all: neither by heaven, for it is God’s throne; 35 nor by the earth, for it is His footstool; nor by Jerusalem, for it is the city of the great King. 36 Nor shall you swear by your head, because you cannot make one hair white or black. 37 But let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No.’ For whatever is more than these is from the evil one. (Matthew 5:33-37, NKJV)
Jesus knows there are people who think what they say is only binding when they give their word with an oath. Without it, they feel at ease to break their word (see Matthew 23:16-22 for examples of this). Such people still exist. Honesty holds little value to them, so they break their word easily and repeatedly. Apparently, they think by emphasizing or exaggerating their honesty they increase their integrity and credibility. So, they swear by God, by heaven, by earth, and by many other things. They assure you they are telling you the truth as they say, “I swear…” For Christians, a simple “yes” or “no” is enough to establish the truthfulness of our words. Jesus said, “more than these is from the evil one.” Be the person whose integrity of heart means your word is your bond. Then, when you speak, others never need to wonder whether you are telling them the truth. (Revised, Sword Tips #320)
Sword Tips 