I'm assuming you are referring to "The Voice You Hear When You Read Silently" by Thomas Lux. If this is not the poem to which you are referring, please post again with a more complete identification of the work about which you are asking.
"The Voice You Hear When You Read Silently" is illustrating the ways in which we all add our own personal experiences and meanings to the written words we read on the page. Because of the background knowledge and events in our lives, certain words (such as "barn" in the poem) carry added significance when we read them. Those added meanings will be different for every reader, even when they are reading the exact same text, since the experiences creating those meanings will be unique.