The importance of English
English is a language with an extremely diverse history, and its development into a full-fledged tongue was one that was influenced by many other languages. Its inclusiveness and modular nature mean that it is a language that is constantly changing and growing bigger, and it includes many loanwords from other cultures; these factors make it one of the fastest-growing languages in the world. It is growing in popularity, too, as defined by the number of people who speak it. At least 400 million people speak English as their first language, and that number is only the beginning. A recent estimate states that non-native speakers of English outnumber those for whom it is their first language by a factor of three to one. These numbers combined represent over a quarter of the entire world's population. This is part of the reason why English is a very rewarding language.
It is a well-known fact that Mandarin Chinese is the most commonly-spoken language on the planet, but there is a caveat. Mandarin Chinese is only really spoken in China, whereas English speakers are spread widely throughout the world. This is one of the main benefits to learning English as a second language. Since so many other people speak it, and in such disparate areas, it vastly increases your chances of being able to communicate with as many people as possible. Statistics show that it is the language most commonly taught as a foreign language, so choosing to learn it yourself opens up a very wide range of communicability options.
Another reason to learn English is the fact that increasing amounts of worldwide business are being conducted in English. With the advent of outsourcing, for example, people in various countries are being given the opportunity to work based on their capacity to speak English. Even leaving aside the fact that bilingualism is always a useful skill, the scope for employment is much wider for those who speak English in foreign countries. English, also, is the language in which the sciences are most often discussed and presented. A study done in 1997 indicated that 95% of scientific publications and submissions, even at that time, were done in English. An even more surprising fact is that only 50% of those submissions came from countries in which English was the dominant language.
A final reason, which many would claim is the most important, is that the English-speaking literary and cinematic landscape is so wide-reaching and diverse that watching or reading them in their native language serves to both educate and entertain you. Some of the seminal literature of all time, such as the works of William Shakespeare, is written in English. His plays and poems are regarded by many to be necessary reading, and due to the nature of the writing, translations of his works are often impossible. Of course, there is great literature in every language, but the sheer wealth of choice in English-speaking entertainment is a great reward in and of itself.
These are only some of the reasons that the learning English is a wise thing to do. There are many more examples of the importance of English, but the above should be more than enough to tell you that if you want to have choices in life, learning English is one of the best ways to accomplish that.