“Actions speak louder than words.”
When we send a message as part of a communication, it can reach the receiver in more than one way: through the words (verbal channel) we use, through the voice(vocal channel) we use and through the body language (action channel or what is broadly considered as ‘non-verbal’ channel).
Imagine you are writing a letter to a person A, talking to a person B over phone and meeting a person C face-to-face and trying to convey the same message in all the three cases. Who do you think would receive the message most clearly? in all likelihood it is person C.