Why Does This Matter?
If your site doesn't have an SSL certificate, you will find it difficult to get traffic to your website, much less get visitors to enter their credit card information and personal details.
When a user visits a website, the major web browsers will let that user know that the site they're on isn't secure. Take the University of Florida's site, for example. Google Chrome (the browser in the below image) displays a clear ‘Not secure' message to any user that finds themself on a website without an SSL certificate with a validity period deemed safe. Due to UF's reputation and the thousands of people that use the site safely every day, Google Chrome's message may not influence people to leave the site.
This is not true of smaller businesses or websites that offer some form of ecommerce. Without a sterling reputation and proof of safety, many would-be customers will simply leave your site, trusting it is, indeed, not secure. Chrome tells them as much when they click to learn more.