Have you ever had someone try to persuade you of their sincerity by saying "I swear"? Or, I love this one, "To be honest..." How about, "I am telling you the truth such and such happened." Or there is, "Honest to God..." These are common expressions of trying to persuade someone that the speaker is speaking the truth.
When someone says to me, "To be honest," or something similar I think, aren't you always honest? James tells us that we should never use these kinds of idioms but simply speak truth all the time. Our yes should always mean yes and our no should always mean no (James 5:12).
When we always speak truth, we do not need to convince someone. They will know we are speaking truth because that is our habit.
