Ever since Google search engine came into existence, it has been the most sought after source of traffic for webmasters mainly because of its highly targeted nature. The key to getting ranked in the Google search engine for important keywords is link building. Every link to a website is considered as a vote by one website to another.
Link building is a highly evolved method of SEO. Gone are the days where you can easily obtain a link for free. Today, people buy blog posts. Since blog posts provide contextual back links, they are considered as the links with the highest quality. If the PR of the blog post is high, the link is that much better.