Whenever the believer speaks, it should bring Life; that which edifies the body. No blasphemy, slander, or faithlessness should proceed out of the mouth of a believer. Our words have to build up our brother's spirit, not tear it down. They are to edify, not only the body of Christ, but all who hear.
"Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may Minister Grace unto the hearers (Ephesians 4:29).