Symbolism, Imagery, Allegory
There are plenty of place names that have become infused with metaphor. There's Zion. There's Rome. There's Mecca. There's even Brooklyn.
All of those real-life geographical locations have been given additional meanings: "all roads lead to Rome," "Yosemite is a Mecca for nature lovers," "Silver Lake is the Brooklyn of Los Angeles."
But the Caco women take it to the next level: the afterlife.
Both Atie and Sophie refer to "Guinea" as the place that they'll go after death to be reunited with all the women of the Caco family. But Guinea is more than just a supernatural location where generations of awesome women hang out, or a part of Haitian mythology. It's an actual, geographical location, something that Sophie can see on the horizon as she returns to the U.S. with her mother:
[...] the hill in the distance, the place that Tante Atie called Guinea. A place where all the women in my family hoped to eventually meet one another, at the very end of each of our journeys. (27.174)
Guinea is also the place of origin, where all souls are created and myths are made. Atie shares the story of the Sky Bearers with Sophie when she is trying to explain "chagrin," the condition that might make Grandmè Ifé fall into despair if she gets too attached to Sophie before she leaves:
They are the people of Creation. Strong, tall, and mighty people who can bear anything. Their Maker, she said, gives them the sky to carry because they are strong. These people do not know who they are, but if you see a lot of trouble in your life, it is because you were chosen to carry part of the sky on your head. (3.25)
Like the Heaven of Christianity, Guinea is meant to be a source of comfort for believers. For the Caco women, it's the meeting-place of ancestors in the next world as it was in this one—many Haitians claim ancestry from the Guinea Coast of Africa. It is no wonder then that going to Guinea is the equivalent of going home.