Osho was a spiritual teacher active in both India and the United States. He died in 1990.
Osho (also known as Bhagwan) became controversial due to his provocative and frivolous behaviour. On Youtube, there are several clips showing Osho spouting expensive wrist watches (probably quite deliberately), cracking lewd jokes, or claiming that alcohol is allowed at his ashram, since alcohol is vegetarian! His message sounds very "hippie", almost libertarian or libertine.
This book, by contrast, shows Osho in a surprisingly somber and intellectual mood. He does crack jokes from time to time, usually featuring the Muslim satirical character Mulla Nasruddin, but overall, he sounds more serious in "The Mustard Seed" than he does on Youtube. He also sounds less libertine than in some of his other written works.
"The Mustard Seed" is a collection of talks, recorded and later written down by Osho's followers. Since the Osho International Foundation wants to put forward Osho's message as timeless, none of the speeches are dated. This is a problem, since the Osho movement did change over the years. Periodically, it was more closed and cultish, and at other times, more open. At least critical readers would want to know the context of Osho's remarks.
The contents of the book are far-reaching. Frankly, the man speaks about everything! The main theme is how to reach spiritual enlightenment, that "God" is within each of us, that we can find "God" if only we let go of worldly desires and seek fulfilment through meditation. Osho claims that this was the original message of Jesus, and attempts to prove this by quoting and interpreting the Gospel of Thomas, a Gnostic apocryphon not included in the official Christian Bible. While a few scholars consider the Gospel of Thomas to be based on early material, most are of the opinion that this text was written much later than the Biblical Gospels, and thus cannot contain the real message of Christ. Of course, this is of little consequence to Osho and *his* message, which stands on its own, even without the Gospel of Thomas. Still, it's not a co-incidence that Osho has choosen this particular document for comment. The Gospel of Thomas may not have been the true message of Jesus Christ, but the work does fit admirably well with "Eastern" forms of spirituality.
The most annoying statement in "The Mustard Seed" is Osho's claim that the Jews suffer because of their crucifixion of Jesus. Anti-Semitism? Perhaps, but Osho sounds equally anti-Christian and anti-Hindu. He says that Jews should claim Jesus, since Jesus, after all, was a Jew, not a Christian! His statement that the Hindus are better than the Jews since the Hindus never killed the Buddha, is surely intended as sarcasm. In reality, Osho and his fellow Hindus had very cold feelings towards each other, apparently one of the reasons why Osho later moved to the US.
The main problem with "The Mustard Seed" (apart from the weird typeface, making the book somewhat difficult to read) is that it doesn't sound very Oshoite. If you want vintage Osho, read "Freedom", "Courage" or "Sex Matters". Or listen to his Youtube appearances!