The reason for this command is given: We are not to swear “by the heaven, for it is the throne of God; nor by the earth, for it is the footstool of His feet; nor by Jerusalem, for it is the city of the great King. Neither shalt thou swear by thy head, for thou canst not make one hair white or black.” R.V. MB 66.1
All things come of God. We have nothing that we have not received; and, more than this, we have nothing that has not been purchased for us by the blood of Christ. Everything we possess comes to us stamped with the cross, bought with the blood that is precious above all estimate, because it is the life of God. Hence there is nothing that we have a right to pledge, as if it were our own, for the fulfillment of our word. MB 66.2
The Jews understood the third commandment as prohibiting the profane use of the name of God; but they thought themselves at liberty to employ other oaths. Oath taking was common among them. Through Moses they had been forbidden to swear falsely, but they had many devices for freeing themselves from the obligation imposed by an oath. They did not fear to indulge in what was really profanity, nor did they shrink from perjury so long as it was veiled by some technical evasion of the law. MB 66.3
Jesus condemned their practices, declaring that their custom in oath taking was a transgression of the commandment of God. Our Saviour did not, however, forbid the use of the judicial oath, in which God is solemnly called to witness that what is said is truth and nothing but the truth. Jesus Himself, at His trial before the Sanhedrin, did not refuse to testify under oath. The high priest said unto Him, “I adjure Thee by the living God, that Thou tell us whether Thou be the Christ, the Son of God.” Jesus answered, “Thou hast said.” Matthew 26:63, 64. Had Christ in the Sermon on the Mount condemned the judicial oath, He would at His trial have reproved the high priest and thus, for the benefit of His followers, have enforced His own teaching. MB 66.4
There are very many who do not fear to deceive their fellow men, but they have been taught, and have been impressed by the Spirit of God, that it is a fearful thing to lie to their Maker. When put under oath they are made to feel that they are not testifying merely before men, but before God; that if they bear false witness, it is to Him who reads the heart and who knows the exact truth. The knowledge of the fearful judgments that have followed this sin has a restraining influence upon them. MB 67.1
But if there is anyone who can consistently testify under oath, it is the Christian. He lives constantly as in the presence of God, knowing that every thought is open to the eyes of Him with whom we have to do; and when required to do so in a lawful manner, it is right for him to appeal to God as a witness that what he says is the truth, and nothing but the truth. MB 67.2
Jesus proceeded to lay down a principle that would make oath taking needless. He teaches that the exact truth should be the law of speech. “Let your speech be, Yea, yea; Nay, nay: and whatsoever is more than these is of the evil one.” R.V. MB 67.3
These words condemn all those meaningless phrases and expletives that border on profanity. They condemn the deceptive compliments, the evasion of truth, the flattering phrases, the exaggerations, the misrepresentations in trade, that are current in society and in the business world. They teach that no one who tries to appear what he is not, or whose words do not convey the real sentiment of his heart, can be called truthful. MB 68.1
If these words of Christ were heeded, they would check the utterance of evil surmising and unkind criticism; for in commenting upon the actions and motives of another, who can be certain of speaking the exact truth? How often pride, passion, personal resentment, color the impression given! A glance, a word, even an intonation of the voice, may be vital with falsehood. Even facts may be so stated as to convey a false impression. And “whatsoever is more than” truth, “is of the evil one.” MB 68.2
Everything that Christians do should be as transparent as the sunlight. Truth is of God; deception, in every one of its myriad forms, is of Satan; and whoever in any way departs from the straight line of truth is betraying himself into the power of the wicked one. Yet it is not a light or an easy thing to speak the exact truth. We cannot speak the truth unless we know the truth; and how often preconceived opinions, mental bias, imperfect knowledge, errors of judgment, prevent a right understanding of matters with which we have to do! We cannot speak the truth unless our minds are continually guided by Him who is truth. MB 68.3
Through the apostle Paul, Christ bids us, “Let your speech be alway with grace.” “Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.” Colossians 4:6; Ephesians 4:29. In the light of these scriptures the words of Christ upon the mount are seen to condemn jesting, trifling, and unchaste conversation. They require that our words should be not only truthful, but pure. MB 68.4
Those who have learned of Christ will “have no fellowship with the unfruitful works of darkness.” Ephesians 5:11. In speech, as in life, they will be simple, straightforward, and true; for they are preparing for the fellowship of those holy ones in whose mouth “was found no guile.” Revelation 14:5. MB 69.1