When you looking for real engagements of your website visitors and want them to come back often, read your articles, trust your opinions or sell something to them, you need a lot of organic traffic.
Definition of organic traffic is: real visitors (real people) who visiting your blog and they can be gained from organic search results on search engines like Google, Bing, Yahoo... Or from social media websites like Facebook, Twitter, Google Plus, Pinterest etc... But also can be visitors from referring websites where you have backlinks to your blog.
Once you build trust of your websites and make your visitors to come back, read more articles or buy more of your services / products, you get more direct traffic (traffic from someone typing your URL into their browser to visit your blog).
That's where all factors of off-page SEO are important. Get quality backlinks to get more exposure on other blogs or social media websites, then it will also bump positioning your website in search engines result pages (SERP) where you get even more organic traffic.
It can be also gained by frequent emailing your blog members if you built your email list and other various methods where you get real visitors and real clicks to convert your website into trustworthy source of information or business.