in Basic, if you didn't have a line number, how can you preform a
GOTO 10
that was a way to jump lines, a good way that was found ... more than 20 years ago!
today, the lines help us catching errors/exceptions because the debug engines are made to send us in the message that we got an exception on line xxx and we jump right away to it!
imagine a world without line numbers... how can a reporter be paid without the lines?
"Now that you know the novel, you have to write a summary with no more than 50 lines"
remember this? Even at the school we learn about line numbers!
if it wasn't invented, someone will already invented again so we could use it nicely :)