The book was a break-through best-seller, attracting many readers who did not ordinarily choose science fiction. Soon it became quite popular among the late-1960s counterculture -- some aspects of hippie philosophy were influenced by this book, most notably Smith's advocacy of sexual freedom and liberation. Rumor has it that the book was a favourite of Charles Manson, who used some ideas from the book in his own commune.
When Heinlein first wrote Stranger, his editors considered it far too lengthy, and required him to cut it by several thousand words before it could be published. Also cut was a sex scene considered too controversial for the day. This 1962 publication received a Hugo Award, and stood for almost thirty years. After Heinlein's 1988 death, his wife Virginia found a market for the "uncut" edition, which was published in 1991. Critics disagree as to which edition is preferable.
A Novel of Consequence Like many influential works of literature, Stranger made a contribution to the language: specifically, the word "grok." In Heinlein's invented Martian language, "grok" literally means "to drink" and figuratively means "to understand," "to love," or "to be one with." This word rapidly became common parlance among SF fans, hippies, and computer hackers, and has since entered the Oxford English Dictionary among others.
A central element of the latter half of the novel is the religious movement the Martian-born Smith founds, the "Church of All Worlds." This church is an initiatory mystery religion blending elements of paganism and revivalism with psychic training and the teaching of the uniquely magical Martian language. In 1968, a group of neopagans inspired by Stranger took it upon themselves to found a religious group with this name, modeled in many ways after the fictional organization. Their Church of All Worlds[?] remains an active part of the neopagan community today.
On a lighter note, Stranger is also often cited as containing the first description of the waterbed[?], an invention which made its real-world debut a few years later in 1968. The "inventor" who brought a waterbed design to the United States Patent Office was refused a patent on the grounds that Heinlein's descriptions in Stranger and another novel, Double Star, constituted prior art[?].  (http://ebbs.english.vt.edu/20th/txts/heinlein/heinlein.lore)
Interpretations Many readers believe Heinlein wrote a number of puzzles into the work. One, regarding the naming of the characters, is described in the introduction to the uncut edition. A number of readers have seen deeper mysteries in it, particularly since it is such an uncharacteristic work for its author. (Though nontraditional sexual relations and a certain ethical anarchist attitude pervade many of Heinlein's works, scant few could be regarded as mystical.)  (http://www.wegrokit.com/thelema.htm)