John Beyond the Golden Rule, which is something that was already pretty universal and predates the Bible by hundreds of years, what moral
advice the Bible gives is hopelessly
outdated, and it's message of a preferred people, be they Jew or Christian, is
really rather elitist.
(However, please do not forward your copy of the book to them, as we will not be able to notify them of updates when we make them, and we
really don't want people using
outdated advice.)