Ephesians 4:25 Therefore, having put away falsehood, let each one of you speak the truth with his neighbor, for we are members one of another.
In order for the human body to make a right diagnosis of itself, it needs to tell itself the truth. It does no good for the brain to tell the neck that there is no pain if indeed there is pain. Lying to yourself in regards to your condition could be a grave and deadly mistake. The body will not function for long if it is filled with lies.
When we come to Jesus, we come by laying down (among many things) our lies. The text assumes that becoming a Christian means that you have put away falsehood. Since you are in Christ, and have put away falsehood; the next step is to speak the truth in love. Christians are all members of one universal church. And no correct diagnosis will occur when we speak lies one to another.
Go forth this day having girded around your waist the belt of truth! This belt does more than just hold your pants up; it brings unity to the body of Christ.