Why was the need for script …

It turns out that there is no special reason for making block and small letters. 

Capital letters were the earliest form of writing in ancient alphabets, date back to the 3rd. century BC in Greece. 

The different shapes of the lowercase letters developed gradually through transformations of the capital letters by the elimination of a part of the letter (see ‘b’-beta in Greek- from B) or by lengthening a part of it ( see ‘d’ –delta in Greek- from D). 

Small letters were used to write faster on papyrus and parchment. 

Now capital letters serve several purposes in English. One of the main purposes is that they help us see when a new sentence starts. They also help us see when a word is a name, instead of just an ordinary noun. They can also often help us see when a string of words is the title of a movie or book, and not just a regular sentence.