English is the most commonly spoken language in the world.
Knowing English means that you can understand and be understood almost everywhere in the world. English is also the "language of opportunities", it opens the door to the world since it is the international language of communication, commerce, internet and computers, science, tourism and travel business and many many more sectors.
Learning to speak English well may be the best thing one can do to improve his/her life. It has countless benefits and advantages that affect our lives and our thinking about the world.
It gives access to knowledge: most pages on the web are in English or can be read in English, most books can be read - even if they are not by a native English author - in English, and also the language of the major international news channels and newspapers is English. And not to mention science and technology, two key sectors where English is basically the working language.
Another aspect is that English is spoken worldwide and by many people. If you can communicate in English, you can contact people from all over the world and travel more easily as well, English is spoken in more than 100 countries.
Speaking English is an added value on the job market, and in some sectors it is inevitable, especially in the business, science and technology sectors.
And maybe the most favorable characteristic of English is that it is easy to learn. It is not only because its grammar is less complicated than most of other languages' or because its sounds are (mostly) easy to pronounce but also because it is everywhere. It is impossible to avoid English, it is around us, we find it when we go to the cinema, when we listen to music, when we watch television when we turn on the the computer, when we travel, when we work or when we make friends.
With English limits and borders disappear.