English has become, to a large degree, the international language of business and science. These alone make it an important language to learn. Additionally, the United States and Great Britain have some of the world's best universities, and if someone wishes to reap the benefit of their educational offerings, it is necessary to learn English. Finally, some of the greatest literature in the world is written in the English language, and while translations are often available, nothing is as good as reading fine literature in its original language.
As to learning the history of English, there are many reasons to do so. Learning the history of a language helps you learn the language better. And this is true even if English is your native language. And also true is that it helps you learn about other languages, too. What is so wonderful about English is that it has incorporated words from all over the world. Every time the British Isles were conquered, by the Danes, the Romans, and the Normans, instead of speaking the language of the conquerors, the English absorbed some of their language and made it part of their own. Every time the British sailed to a new land, they absorbed new words into their language. So, in some ways, the history of English is the history of much of the world. It is fascinating to learn how English evolved and the history of so many of its words. Our words tell little stories. For example, "algebra" is an Arabic word. The whole idea of this kind of math is from the Arabs. A sandwich was supposedly invented by the Earl of Sandwich, who is said to have wanted to easily eat something without having to leave the gambling tables. So many of our words and expressions have colorful histories like this. For me, this is part of the delight of English, and I hope it becomes thus for you, too.
Many people all over the world are motivated to learn English, which has become an important part of getting along in our global village. Learning the history of the language helps us to learn the language even better, in such a fascinating way.