The soul is the divine aspect of yourself; the elementally pure & untouched part of you which will live on throughout eternity. It is not to be confused with your spirit which is an entirely different thing. Your soul is the aspect of yourself which makes you who you are at the core; the unchangeable aspects.
This binding protects anyone from intentionally or unintentionally binding on your soul. Again, this is not to be confused with your spirit as your spirit is what reincarnates and moves from life-to-life being born again and again. It is also what most practitioners bind to when you do not want a physical vessel. This binding is not about spirit bindings, it is about soul bindings.
The power behind this binding will keep people from binding to your soul and corrupting the purity of the divine.