Why is English full of synonyms?

What we call "English" today is a language that has its roots in many different languages, brought together by the people who lived at one point or another (in the past dozen or more centuries) in England. For the most part, there are "romance" contributions from several romanic languages, many of which derive from Latin, and can be traced back to Roman occupation of parts of today's England. The other major contribution is "Saxon", stemming from the language of Saxons. There are also Germanic, Celtic and other contributions...

Since a language develops during its use, by the people who use it, and since very diverse peoples have been using the language we today call English, there is a large amount of redundancy. People tend to stick to what they know, adopt redundant Words in order to be able to communicate with the neighbors, and after a few generations, its all part of the same language. In addition, literature (and also science) uses the added wealth of synonyms and near-synonyms to express subtle differences (speed, velocity, rapidity, rate,...). This in turn (sometimes) becomes adopted in spoken language and amplifies the expressive power of the language.