A.T. Robertson 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 (μη ομοσα ολως). More exactly "not to swear at all" (indirect command, and aorist infinitive). Certainly Jesus does not prohibit oaths in a court of justice for he himself answered Caiaphas on oath. Paul made solemn appeals to God (1 Thessalonians 5:27; 1 Corinthians 15:31). Jesus prohibits all forms of profanity. The Jews were past-masters in the art of splitting hairs about allowable and forbidden oaths or forms of profanity just as modern Christians employ a great variety of vernacular "cuss-words" and excuse themselves because they do not use the more flagrant forms.