Why is swearing a roadblock to honesty? What is the problem with swearing oaths (Mt 5:33-37; Js 5:12)?
Oaths divide speech into two camps — honest speech, and less honest speech.
It is not that the oath is in itself wrong, but that it divides speech into two levels. Some statements are sworn to and thus must be true, while others are just normal speech and may not be. … Oaths are dangerous, for they make some speech more honest than other speech. (Peter Davids)
As such, to use an oath (or to swear) is to admit that you are someone who is normally dishonest, someone who can’t be trusted. It is an admission that, outside of using oaths, you are a less than trustworthy person, that your commitment to truth is suspect and needs to be buttressed and strengthened. Oaths are only needed because your speech is unreliable.
Swearing (i.e., oath-taking) is really a pathetic confession of our own dishonesty. Why do we find it necessary to introduce our promises by some tremendous formula? … The only reason is that we know our simple word is not likely to be trusted. (John Stott)
Oaths seems to imply that some speech is more lax and less serious with regards to honesty. The use of oaths implicitly downgrades the expectations for honesty elsewhere. But we are a people who believe that all speech is binding — we are held accountable for the integrity all of our speech, not just sworn speech.
Thus, as people who are called to absolute honesty, swearing and oaths should have no place among Christians. Our commitment to truth should be so consistent and dependable that there is no need for us to buttress our speech with swearing or taking oaths. Our plain speech is good enough. It’s trustworthy as it is.
Kirk E. Miller 