Our tone of voice is closely linked to our emotional response to a reading. For our proclamation to be authentic, our emotional response to the message in the reading needs to be an authentic echo of the emotion in the reading itself. So, before proclaiming we need to discern the message and its emotion, and through reflective prayer absorb what we read.
Some readings call for a quiet intensity, in others there can be disappointment, or sorrow, or rejoicing, or determination, or submission.
If we have no emotional response to a reading our voices will betray us with a neutral, boring tone. The reading will not be a proclamation and the chances of its registering with the congregation are greatly diminished.