#2 Star Trek by Vonda N. McIntyre 1986

One of the best underlying messages I see in Star Trek is the acceptance of culturally different people. Being a xenophobe is enough to get you kicked out of the Starfleet and all different forms of beings have to coexist. Mr. Spock is always trying to decipher human emotions and one of the more predator-like crew members was outraged at the fact one man kept a wild cat as a pet. One secretary took her nervousness to the extreme but once you realize that she had a troubled past, was trying to support her two younger brothers, and hiding the fact that she was really three years younger than she said she was, that nervousness becomes understandable. 

Closer to the end of the book the Enterprise stumbles across a species no one has encountered before. They travel in a far more advanced ship; one that takes on the form of a small world. Their kind did not build it and nor does anyone run it. There are no leaders either, they live their lives as the please. Communicating is difficult because neither species can make sense of the other. 

Understanding others is what I pinpointed as the books theme.  Even in ordinary situations and every day conversations it is essential to know the character of the person whom you are speaking with. Otherwise offence could be taken from things not intended to be offensive or the point you are making meaningless. Like everyone would always tell you when you were little: It is good to be unique. We each add something different to the world that makes our lives run as we know it.