I am honored to write on this subject, because I think sisters are so important. I am an only child, but the mother of nine children, and I have had the joy of watching my children love each other. I have five daughters, and have always stressed to my kids that the most important relationship they have is with each other. Their love, friendship, and support will outlive me, their boyfriends, marriages, and even other friends. Sisterhood (even if it means best girlfriends) is vitally important. And sure, they sometimes make you mad and forget to give back the skirt they borrowed, but hopefully they'll always be there for you when the chips are down. The sisterhood between blood sisters or sister-like friends is a sacred bond. They will (or at least should) love you, forgive you, support you even when they think (and you know) you've done something terribly stupid.
Being able to forgive each other is vitally important in this bond. You need to be honest with each other and have integrity and mutual respect-even when that's hard. (Like not stealing each other's boyfriends! My girls have a pact about that, which has served them well. Ex-boyfriends and even past dates are off-limits.) Everything you can do to help a sister will come back to you a thousandfold.
Sometimes we are related to people we don't like or understand, with whom we have nothing in common. Or you may be an only child. In that case, you choose special friends who become your sisters. They are the best friends you take to your heart. If you choose well, they will be your friends for life. They can carry you through tough times, and you will do the same for them. My best women friends are the sisters I never had. And I got to choose them! Even the sisters who drive you crazy when you're young, will turn out to be your best friends in the end. Sisters are forever.