Charles Ellicott Commentary Matthew 5:34

"but I say unto you, swear not at all; neither by the heaven, for it is the throne of God;" — Matthew 5:34 (ASV)

Swear not at all — Many interpreters, and even entire Christian communities such as the Society of Friends, see in these words and in James 5:12 a formal prohibition of all oaths, whether promissory or for giving evidence. They view the general practice of Christians, and the formal teaching of the Church of England in her Articles (Article 39), as simply a compromise with evil.

The first impression made by the words is indeed so strongly in favor of their position that their scruples should be treated with great sensitivity, as English law has finally done. However, their conclusion is believed to be mistaken for the following reasons:

1. If it were true, our Lord would be directly repealing part of the moral law given by Moses, instead of completing and expanding it, as He did with the Sixth and Seventh Commandments. He would be destroying, not fulfilling.
2. Our Lord Himself, after having been silent, answered a solemn, formal oath (Matthew 26:63–64), and the Apostle Paul repeatedly uses such forms of sworn testimony (Romans 1:9; 1 Corinthians 15:31; 2 Corinthians 1:23; Galatians 1:20; Philippians 1:8).
3. The context shows that the sin our Lord condemned was the casual use of oaths in common speech, with no real thought as to their meaning.

Such oaths were inherently irreverent and therefore inconsistent with the fear of God. The real purpose of an oath is to intensify that fear by making people intensely aware of God’s presence at the very moment the oath is taken. Oaths are therefore rightly used when they achieve that purpose.

In practice, it must be admitted that the excessive use of oaths on trivial occasions, both for giving evidence and for making promises, has tended and still tends to weaken awe and undermine reverence for truth. We can rejoice when their number is reduced. In an ideal Christian society, no oaths would be needed, for every word would be spoken as if by those who know the Eternal Judge is listening.