Those who attempt to learn Arabic are probably familiar with the specific challenges associated with learning this language. One of the greatest challenges that students of Arabic are faced with has to do with the script. The Arabic language has an alphabet that contains 28 letters. Most students find that it does not take long to learn the Arabic alphabet. However, each letter has four different forms. The form that is used depends on whether the letter comes at the beginning, middle, or end of a word. Learning the different letter variations can be a challenge for students. Another characteristic of Arabic that may confound students at first has to do with how books are written and read. In Arabic, books are read from the right to the left. When a book is opened, it is opened from the left.

One of the greatest challenges that most students face as the learn Arabic is the fact that most vowels are not used when writing. In beginning textbooks, the missing vowels are indicated by little marks that are placed above and below the words. However, more advanced texts and most reading materials do not contain these helping marks. Yet another challenge involves the special "noises" that one must learn in the study of Arabic. Learning Arabic involves learning many new sounds that are not used by most Westerners. Perhaps the most infamous of these is the sound that is described as emitting air from the back of your throat, as if trying to put out a candle by blowing air from the throat. This sound can be difficult for new students to learn and to use fluidly during conversation.
Finally, learning new vocabulary poses a special challenge for those who seek to learn Arabic. For Westerners, studying European languages seems easier for students because they tend to recognized vocabulary words. The language "feels" more familiar, and thus does not seem to represent such a challenge. Although there are special challenges to learning Arabic, the effort is definitely worth it.

Arabic is the language of a large part of our planet. It is the main language in 22 countries, spoken by more than 250 million people. It is also the second language in many Islamic countries because It is considered the spiritual language of Islam -one of the world's major religions- (we're talking here about more than 1 billion people). It is one of the permanent languages in the United Nations. Another reason is that Arabic is one of the oldest living languages in the world, and it is the origin of many languages, in fact there is a theory that says "Arabic is the origin of languages" and those who adopt this theory depend on the fact that Arabs are able to pronounce any sound in any language in the world very easily, on the other hand lots of non-Arabs have a very hard time pronouncing some Arabic letters which are not available in their native language.

Source: http://www.socialstudieshelp.com/topics/learn-arabic.html
and http://www.arabion.net/learnarabic.html