Let us look at where the tradition of secrecy comes from. Mystical texts historically have been written by scholars (mostly men and mostly rich) and priests. The cabala, for example is an esoteric set of works of interest mostly to scholars, and alchemists.
The medieval alchemists used mystical texts as the basis for their work. However, their work was heavily concerned with turning lead into gold (actually turning any cheap material into any expensive material) and their books contained their recipes. Alchemical recipes were kept secret for the same reason modern corporations keep industrial secrets. Another reason for secrecy was a healthy fear of the Church. Any written evidence of heresy (deviation from the policies of the Church.) could get one burned at the stake (In England and America heretics and Witches were hung not burned.)
Secret societies such as the Masons also placed a high value on secrets as part of their group bonding. Retaining knowledge in the hands of a select few individuals is a "power over" technique that is very popular among hierarchical institutions from the Brahmins to the Levite priests to the Druids to the Catholic Church. Starhawk discuses this at length and in detail in "Truth or Dare".
However, all that it is not the legacy of the shamanic traditions.
Witchcraft was a religion of people who coax life from the earth. It was a religion of farmers and midwives. Literacy was never a priority among those people or even an option. Shamanic traditions tend to be oral, hearth fire stories and lullabies, casual magic to bring good fortune and ward off bad, these things are not written in books.
Book are inherently intellectual, they exist in the mind. The Craft is intuitive, it comes from experience, and you must do to know, the knowledge exists in the body of the person who has experienced it.
There are thousands of magical books on the market many of them contain information similar to this Book of Shadows. None of them are exactly like this one. We have no secrets to reveal only mysteries, and mysteries keep themselves.
How do these concepts apply to a magical text?
A magical text is a shadow cast on the wall of the cave of our perception by the fires of reality that burn at the mouth of the cave. Ritual is the tool we use to unite with the greater truths of our existence. The written record of the ritual is the shadow it casts. The Ritual is the substance, the Greater Truth is the light, and this site is a Book of Shadows.
There is another meaning for a "Book of Shadows". It is a journal where you record all your experiences in ritual. We recommend that you keep one. Five years from now you will appreciate being able to look back on previous rituals, and remember who did what when.
The science of Magic is based on personal resonance with symbols. In order to work a spell the Witch must have an intimate and personal relationship with the symbols she is working. No two people have the same set of relationships and correspondences therefore it is necessary for each Witch to write her own Book of Shadows recording her correspondences and rewriting other peoples spells. The personal nature of Grimoires (books of Gramarye) is well documented, a spell that works well for one person can look like total gibberish to another.