Each of us is a radar machine constantly scoping out our environment. Human beings are sensitive to body language, facial expression, posture, movement, tone of voice and more. To effectively communicate, these interpersonal communication dynamics must match your words. Words are distantly useful for people who are scoping out the meaning of a communication.
Without awareness of the whole person, who is doing the communicating, including the factors in interpersonal communication dynamics, you miss much of what is being communicated. At the same time, if you communicate without understanding all of the interpersonal communication dynamics your listener sees and hears, you fail to use powerful aspects of communication.
Your body language, facial expression, posture, movement, and tone of voice can help you emphasize the truth, sincerity, and reliability of your communication. They can also undermine your communication if the words you use are incongruent with the message sent via the interpersonal communication dynamics.
Since communication is shared meaning, your words must send the same message as the other interpersonal communication dynamics. The consistent message ensures effective communication.