Why Algebra?

 ALGEBRA treats quantities as in Arithmetic, but with greater generality. Where in arithmetic we deals with constants ,in Algebra variables be used.

We use different symbols in Algebra ,usually those are alphabets. 

Although above two paragraphs does now answer the Title . Algebra is very useful when we try to figure a universal mathematical law to solve complex calculations. This not only solve our computing time but also helps us to find hidden truth of universe.