“Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, Do not take an oath at all. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil”. (Matthew 5:33-34a; 37)
Swearing and oaths and perjuring basically all come from the same thing, and an oath is simply this: It is making a statement and calling God to witness to the truth of that statement and invoking a curse from God if in fact you’re not telling the truth. We do it, we swear, we say, “I swear to God it’s the truth.” You go into a court, you put your hand on a Bible, “I swear to tell the truth, the whole truth, and nothing but the truth, so help me God.” When you get married, you say, “Before God and these witnesses, I take thee,” and you are invoking God as a witness to the veracity of a lifelong vow that you’re making.
Truth knows no degrees, no grays, only black and white, and half-truths are whole lies. The Bible says you’re not to lie. “There are six things the Lord hates, yea seven. The first is a proud look and the second is a” – what? – “lying tongue.”
If you’re a Christian and you’re a child of the King, you ought to live like one, right? And He is the Father of truth, and when we open our mouth, the truth ought to come out. And on those solemn occasions when we vow a vow to God, we ought to keep that vow. And on those other occasions, in the daily matter of life, our yes should be yes and our no should be no. Anything more than that reveals an evil heart, untrustworthy.
Excerpts from John MacArthur message “The Spiritual Credibility Gap”