Latin has long been the language of the educated. It is the language of science and medicine and, up until the modern era, it was oftentimes used in official documents. It is also very important in Western religion. Latin texts span back to the 3rd Century BC and provide a window into the world of these ancient peoples. Today, though the vulgar languages have displaced it somewhat, Latin remains the lingua franca of science and medicine. When scientists discover a new animal, they still give it a Latin name. For all of its usefulness, it is a dead language, meaning it is not the native, spoken or written language of any currently extant people. Ironically enough, that makes it eminently more useful.
Latin is useful because the meaning of the words never changes. The language is almost completely static. This comes into play when a long span of years is concerned. While "house cat" may take on various meanings at various times, felis silvestris catus will always mean a domestic cat. There is no population speaking this language that will create novel or slang usages of existing words. Latin is vital for scientific and medical businesses. It is also vital to any business that deals with historical matters. Latin's influence is seen on just about every European language, particularly the Romance languages. Its closest surviving relatives are Romanian, Spanish, and Italian, which share a great deal of vocabulary with Latin. Since Ancient Rome ruled the world, this language has been valuable.