From the Boynton Beach Historical Society's Facebook page comes this part of Lake Worth history...

Bryant and Greenwood were the original developers of Lake Worth. These post cards were sent to people in the north to sell 5 acres in the "garden spot of the world." Those five acres were essentially swamp land in the area now known as Greenacres.

Note that the postcard promises that "We give a town lot FREE to each purchaser" of those agricultural lots. It turns out that the "town lots" were the 25 ft. lots in and around our downtown area, which ultimately turned out to be more popular than the agricultural land to the west at the time.