The bond of sisterhood is undoubtedly the most important element in So Long a Letter. It is the golden thread that runs right throughout the story, the unbreakable connection that gives Ramatoulaye and Aissatou the strength to deal with the many trials and tribulations of their lives.
It is only because the two women enjoy such a strong sisterly bond that they're able to confide in each other and share their innermost thoughts, hopes, and dreams. This is a bond of absolute trust, founded on mutual love and respect.
Ramatoulaye and Aissatou have gone through so much together that they know they can trust one another implicitly. This sisterly bond, this special connection that joins them together, was forged when they were teenagers, and has been with them ever since. As Ramatoulaye says in one of her letters:
We walked the same paths from adolescence to maturity, where the past begets the present.
It is this shared experience that has allowed the two friends to deal more effectively with life's numerous ups and downs. Aissatou is divorced and Ramatoulaye is a widow, yet both are able to derive considerable strength from their unbreakable friendship.
In turn, this bond of sisterhood allows the two friends to develop a connection with women as a whole, many of whom have shared the same experiences as themselves. From adversity comes empathy:
I had heard of too many misfortunes of others not to understand my own. There was your own case, Aissatou, the cases of many other women, despised, relegated, or exchanged, who were abandoned like a worn-out our out-dated boubou.
Far from being caught up in their own lives, Ramatoulaye and Aissatou have developed a broad perspective on life that allows them to walk upon their path of friendship alongside countless other women who've gone through the same or similar experiences.