There's a parable that a man goes to a famous rabbi and says "can you teach me the Torah on one foot?"

The wise sage replies, "What is hateful to you, do not do to your neighbor: that is the whole Torah while the rest is commentary; go and learn it"

While not quite as brief, I would say this...if you want to understand the fundamental shift that has occurred in marketing over the past 10 years, read this post from Seth Godin.

Permission Marketing was one of the first marketing books I read and it's been my guiding light since.