I want to also add the position of London as an operational, cultural, financial, and defensive post ever since its creation as a city. Once the newly-called English were in operation, London became a center of commerce. Through London, as a port in front of the River Thames, loads of diverse cultural groups came in and out to make business.The location was prime for trade and exchange,and (as a linguist I can almost ascertain)that the process created its own unique lexicon.

Furthermore, as England expanded as an empire, it brought with it the lexicon of commerce, as well as the cultural gains that London (itself an entire personage far removed from England as a whole) brought with it.

It is not surprising, then, that English became such a powerful language due to the potential of connection that England's capital brought with it, and the influence it exercised in the nearby countries.

The previous posts all correctly point out that English is the lingua franca today, but I don't see where they have addressed how the history of the English language has lead it to become the lingua franca. I'll try my hand at this, but I don't have my usual resources on hand, so I'll have to work from memory. (I recommend the book The Story of English, based on the TV series in the link below. For a more exhaustive linguistic approach, see for example, the outer history section of the textbook by C.M. Millward.)

English was a relatively unimportant language (or, more precisely, a set of dialects) around 450 AD, when a set of Germanic tribes (mostly the Angles, Saxons, and Jutes) moved from their homelands in what is now northern Germany and Denmark to what is now England. Old English was widely spoken on the island in the centuries that followed, lost status when the French-speaking Normans conquered England, and slowly regained status in the late Middle English period. At this point, still, English was just one of many languages. It was generally less respected than Latin among scientists and theologians, for example.

It was not until the period of Early Modern English, a period also known as the Age of Discovery (c. 1500-1800 AD) that English really began to gain status. England began to establish colonies around the world and exported its language and governing systems so that it could import what it wanted, e.g. spices and rare woods and, for a while, slaves. The Early Modern English period witnessed the first time that English was spoken around the world, but still it was not nearly as widely distributed as it is today.

Today English is widely taught around the world as a second language. (The number of native speakers of English is not very large at all, compared to Spanish or Chinese, it's worth noting.) The emergence of the United States as a global power after WWII (incl. the strong economy and the enduring military presence of American soldiers in many countries around the world) took the globalization of English one step further. Still, British English is still widely taught as the prestige form in classrooms around the world.

There's a lot more to say, of course. If you ask for more (e.g. by 'message'), I'll gladly do what I can to help.

I think that the English language is so vitally important because it is spoken in so many parts of the world.  Businesses, educational domains, academic domains, and even realms that deal with security all use English as a language of communication.  In a practical sense, one could survive without English, but with the globalized nature of the world and commerce, knowledge of English is quite essential.  In terms of the appreciation of language and literature, knowledge of English is extremely important in understanding some of the best writings offered.  This is not to say that other languages do not possess the same amount of introspection and talent.  Far from it.  Yet, the knowledge of English could help to open many professional and literary doors.

This is somewhat of an unclear question...

The English language is important to people in many parts of the world because it is their native language.  But I doubt that's what you mean.

The English language is important in the world today because of the dominant position of the United States in an increasingly globalized world.  Because it is important for many countries to do business with the United States, it is helpful for the people of those countries to learn English.

Since this has been true for most of the period since World War II, many people around the world have learned the language.  Since they have, it has become a way that, for example, a French person may speak to a Japanese.  English has become the lingua franca of international business.

I don't know if that's what you mean, though.  Please let us know.