Let's look at how the image is organized, or its composition.  If we use the Rule of Thirds and imagine a grid laid across the image using two horizontal lines and two vertical lines , we discover that the grandfather and granddaughter/homecare worker fall along the intersection of the lines , so we know they are focal points, the two main areas of interest. 

The pile of unopened mail also falls along the intersection of lines , meaning it is also a focal point.  Now we know that the theme of the image revolves around these three areas of focus.

If we divide the image up into foreground, mid-ground, and background, our eyes rest only on details in the mid-ground;  therefore, we know that this is the important area to focus upon in the photograph.