great post by unity100 here on the Law of One.
There are reasons pertaining to the intense preparation and effort that went into preparing Ra contact, involving many incarnations (possibly more than one group like LL) by the away-team and involving an unknown amount of effort on Ra and confederation's side to find, nurture and select a group and then to maintain the contact.
But beyond these, Ra material is the most direct source, unmodified to accommodate the contemporary sentiments of the society and the particular audience which it was intended for, and it is untainted and unmodified by the contemporary or ancient beliefs or biases of current society or earlier societies.
To illustrate simply, if you check any other major channeling material that is popular today, you will see those traits:
Ramtha talks a lot about popular contemporary stuff, considerable religious motifs mixed in - and that is taking out the obvious evidently-tainted stuff like King Kull like atlantis stories and whatnot.
Silver Birch is very, very spiritual. It has a lot of plainly explained and told spiritual examples, lessons and cases, a lot of explained concepts. But it is quite congruent with the old-school spiritualist school that descends from the early 19th century roots. Its quite mystical and, well, 'spiritual' to put it in a way.
Bartholomew is what many people who need acceptance, validation and self esteem, need. Its all about providing 4d energy to those who need it.
Cayce is questionable in that its hard to say that it is a channeled material, for majority of his work is about diagnosing the ailments of people and suggesting treatment. But among these many diagnosis, a lot of spiritual info about the workings of evolution of spirits, their successes and their issues come up as well. Including voluminous amount of historical information. However, it is also colored a lot by the religious beliefs of Cayce himself.
Compared to all of these Ra material is just how things are. Ask something, and the answer is there, clean, clear, direct and blunt. You may like the answer or not. You may understand it or not. You may agree with it or not... It is what it is.
Its untainted and non-colored by any bias, religious or cultural. Some concepts that are used to explain some things are not even known in the contemporary civilization, or are known by very few amount of people (scientists, researches of very particular fields) who may not even have any interest in spiritualist material.
Thanks to the group's work, its well organized as well. It starts from how things start, moves onto history, moves on to how existence works, moves on to contemporary stuff, to near future, and to how things will end (and restart), and then dives into the actual 'secrets' of existing like the archetypes.
One of the best sides is that you can confirm, understand and learn a lot of things by just observing the existing world. By observing current social dynamics or historical dynamics, one can easily observe mechanics of positive and negative conduct, their evolution. Merely by observing people in daily life, one can learn and understand a lot of things about chakras, energies, how these play in interactions of people - from blockages leading to behavioral deviations to the issues and the brilliance those with clear energy centers can manifest.
There is a lot that can be yet told about the usefulness and clarity of this material. I will take this opportunity to stop at this juncture.