Google uses a myriad of factors to decide how websites should be ranked in results for any particular search query, and website owners need to follow a set of key principles and avoid specific practices to make sure that their website ranks highly. In July 2014 Google announced that it's algorithms would begin slightly favoring websites that are secured using HTTPS (HTTP over TLS, or Transport Layer Security).
The general reaction to Google placing importance on HTTPS was mixed, with many wondering why websites that do not feature credit card transactions or even a membership system need to be secured. However, every website benefits from HTTPS, since only by serving data securely can it be guaranteed that content received by the browser has not been altered since leaving the server. By this means, HTTPS lends authenticity both to your website and the content your website serves.
Even though the ranking benefit derived from using HTTPS is likely to be fairly small (Google's Gary Illyes previously described HTTPS as being like a "tie-breaker" between two websites that are virtually identical in all other ranking signals),Google is about to start using changes in it's Chrome browser to encourage more websites to be secured with HTTPS.
Google has openly stated that it's long term plan is to mark all pages served over HTTP as "not secure" in it's Chrome browser. Starting from October 2017 (in version 62) the browser will show this warning for pages with forms served over HTTP. Since it's likely that forms on your website represent the main opportunity for visitors to buy from you or contact you, it's imperative that they are no dissuaded from submitting information to you. In addition, all pages that are not secured using HTTPS will display this warning while using Incognito mode, since those users "likely have increased expectations of privacy".
You should take every opportunity to outperform competitors in search engines, and transitioning to HTTPS is a relatively low-cost way to potentially out-rank your close competitors. In addition, while HTTPS may not be considered to be as important as many other ranking factors, visitors to your website using the Chrome browser will become more and more distrusting of your website as Google's "not secure" warnings intensify.