This is a really beautiful idea to understand. The voice is something completely other than the words that are said. We comprehend more about the person who is talking from their voice and tone often than from the words which they are speaking. This is clear for me to see in my son, only nine months old who now associates sounds with meaning, but does not yet know how to produce words to make his meaning more easily understood.
When we are able to unite the voice and the words, it is akin to speaking our hearts, and we are taught that words that come from the heart enter the hearts of others. All the moreso in our tefilloth when we are expressing our truest desires to HaShem.