SEO is the most important thing for a website. Without it, it is as if you do not have a website.
But You do not want that to happen with your website?
For that, you have to put the book in a library where people can discover it and take advantage of it. just like that book your website needs to be optimized for search engines and google, yahoo and bing are your libraries. you need your website to appear on these search engines so that people can discover you when they search for a problem that you provide solution for.
Just like a library, the books that are on the front get the most attention just like that SEO helps your website to appear on the first page of google.
SEO makes your website famous and thus brings in tons of organic traffic which then turns those visitors into leads and then into business and provides you the opportunity to serve these customers with your business.