James 5:12 KJV
But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation.
The latter part of this verse seems clear enough. Yet, some don’t appear to get it. An example of this is when people – often in prayer – say Lord I confess my sins. Now, you can confess you are a sinner in a single statement. But if you say I confess my sins without actually saying them – your speech is empty. It reminds me of the verses in James 2:15-16 KJV which say, If a brother or sister be naked, and destitute of daily food,  And one of you say unto them, Depart in peace, be ye warmed and filled; notwithstanding ye give them not those things which are needful to the body; what doth it profit?
Let your yes mean yes, and your no mean no. Do what you say and say what you mean.