Good question. Learning English is not the matter of attending classes and passing exams. I believe everyone should learn the English language for the following reasons:
1. English is the main language of news and information in the world.
2. English is the most widely spoken language in the world.
3. In general, the universal language on the Internet is the English.
4. Now online communities like My Space, YouTube, etc., offer people a way to make friends around the world and practice speaking English.
5. It is necessary to learn English if you are planning to study at a foreign university or school.
6. Nowadays in the competitive job market it is necessary to speak English. So if you learn English you will have a better chance of getting a job that pays more.
If you are not motivated to learn English you will become frustrated and give up. Ask yourself the following questions, and be honest:-
1. Why do you need to learn/improve English?
2. Where will you need to use English?
3. What skills do you need to learn/improve? (Reading/Writing/Listening/Speaking)
4. How soon do you need to see results?
5. How much time can you afford to devote to learning English.
6. How much money can you afford to devote to learning English.
7. Do you have a plan or learning strategy?
There are MANY reasons why you NEED to learn English. Here are some links where you can have more reading about why you need to learn English:
Omniglot - Why Learn English
Antimoon - Why Should I Learn A Language?
ESLPartyLand - Why Learn English
Remember, where there's a will there's a way!!