Joe Starks symbolizes for Janie the horizon that Zora Neale Hurston references throughout the novel. The horizon, the farthest point one can see, is a place that holds Janie's hopes and dreams.
In her first marriage to Logan Killicks, Janie is isolated on Logan's farm and is expected to labor in the fields with him all day. At night, when Janie looks at Logan in their bedroom, she is put off by his old age age and dirty feet. She does not find in Logan the "bee to her blossom" that she thought nature had promised her when she had her sexual awakening at the age of sixteen.
Joe Starks meets Janie as she labors on Logan's farm and promises her that she'll never have to work like that again if she leaves with him. Joe is younger, "cityfied," well-mannered, and very ambitious. He tells of his plans to incorporate Eatonville as the first all-black town in America. Joe symbolizes to Janie a broader horizon and expanded dreams. She cannot wait to start a life with him and escape the confines of Logan's farm.
Once in Eatonville, however, Joe begins to control Janie and isolate her from her friends. And although Joe promised Janie an easier working life, she works tirelessly for the general store that Joe built in Eatonville. Their marriage wears away in misery for almost twenty years. The horizon that Joe represented was not as expansive and far-reaching as Janie originally thought.