Instead of nagging my father to lose weight, my mother bought him an extra-large T-shirt imprinted with the message "This space for rent." The primary purpose of this sentence is to

The primary purpose of the sentence was to pass the message to my father that he does not need the excess body space taken up by his excess body weight without making him uncomfortable about it. This sentence is supposed to help him see the need of loosing the excess weight, in comparison to renting out an unused space.