In 2014, BrightEdge published research that showed that 51% of channel traffic came from organic search and that it was far and away the largest channel. In the intervening years there were significant search algorithm changes that dramatically altered the layout and ranking of the search engine results pages and saw an increase in the space taken by Local, Videos, Images, Ads, and Quick Answers.
A good call to action has a clear message and action. It should move people in the direction of purchasing. On a blog post, a good CTA may point people to more in-depth content like an e-book. It can also point people to your products and services. However, the in-depth content is more effective. You can then pitch your product or service using the in-depth content.