The Philosophical Research Society has biography on Manly P. Hall worth reading. It also has links that precis some of his books.
In brief, Manly P. Hall was a 33rd Degree Scottish Rite Mason who also headed the research school of the Rosicrucians at San Jose. He was honoured by The Scottish Rite Journal, who called him 'The Illustrious Manly P. Hall' in September, 1990 and further called him 'Masonry's Greatest Philosopher', saying "The world is a far better place because of Manly Palmer Hall, and we are better persons for having known him and his work."
Here is a quote I was refering to:
"Freemasonry is a fraternity within a fraternity - an outer organization concealing an inner brotherhood of the elect ... it is necessary to establish the existence of these two separate and yet interdependent orders, the one visible and the other invisible. The visible society is a splendid camaraderie of 'free and accepted' men enjoined to devote themselves to ethical, educational, fraternal, patriotic, and humanitarian concerns. The invisible society is a secret and most August (defined as 'of majestic dignity, grandeur') fraternity whose members are dedicated to the service of a mysterious Arcanum (defined as 'a secret, a mystery')." - Manly P. Hall, "Lectures on Ancient Philosophy" (contained in The Secret Teachings of All Ages), p. 433
Albert Pike says the same:
"The Blue Degrees [first, second and third] are but the outer court or portico of the Temple. Part of the symbols are displayed there to the Initiate, but he is intentionally misled by false interpretations. It is not intended that he shall understand them; but it is intended that he shall imagine that he understands them. Their true explication is reserved for the Adepts, the Princes of Masonry (the 28th degree and beyond)." [Morals and Dogma, p. 819]
"Masonry, like all the Religions, all the Mysteries, Hermeticism, and Alchemy, conceals its secrets from all except the Adepts and Sages, or the Elect, and uses false explanations and misinterpretations of its symbols to mislead those who deserve only to be mislead; to conceal the Truth, which it calls light, and draw them away from it." [Morals and Dogma, p. 104-5]
"A Spirit that loves wisdom and contemplates the Truth close at hand, is forced to disguise it, to induce the multitudes [that is you] to accept it... Fictions are necessary to the people, and the Truth becomes deadly to those who are not strong enough to contemplate it in all its brilliance. In fact, what can there be in common between the vile multitude and sublime wisdom? The truth must be kept secret, and the masses need a teaching proportioned to their imperfect reason." [Morals and Dogma, p. 103]
It's often said that Freemasonry has to safeguard its secrets because we, who are part of the "vile multitude", as Pike so charmingly called us, are unworthy to learn the inner truths of Freemasonry but the problem is, in recent times, these inner "truths" have become exposed and, IMO, they are highly controversial and more to do with power and control over the "vile multitude", rather than uplifitng it. Secret handshakes and codes are also part of this secret knowledge.