What is the importance of Number 6 West 57th Street in the nonfiction book, Mornings on Horseback?

Number 6 West 57th Street is the address, at which, Theodore built a house for his family in New York. The home was a lavish showplace, with large rooms, fireplaces, and mirrors. There were inlaid woods, sliding doors, Persian rugs, and tasseled chandeliers.