The first Line tells the computer which interpreter to use while executing the file
Let's say you write a script using python, and while running this script you will use the python interpreter and how would computer know which interpreter to use, it will know through this line which is also called the Shebang, for python
print "Hello world"
let's say again you write a script in bash and you use the shebang for bash script which tell the computer to use the bash interpreter while executing this code
echo "Hello world"
I think it fulfill your need!