Even if the user correctly entered your website's domain name, it can be substituted by hackers.
SSL certificates rule out that possibility: By checking the certificate, the user can be sure that the domain is tied with the real website and not its fake copy.
Furthermore, SSL certificates allow users to check who is the owner of the website. It means that the users can be sure that they visit the website of the right company and not its clone's website.
Another important feature of SSL certificates is Internet connection encryption. Encrypted connection is required to prevent potential theft of confidential data transferred through Internet.