Quality link means a link that in the other website relevant to yours by theme. Though page rank is not the sole factor in having your site rank in the search engine results page, there are greater chances that Google has biases over web pages with page rank than pages that are unranked.

How does page rank work?

There is what we call page rank distribution. SEO experts agree on the fact that page rank is evenly distributed among all pages of the site and all pages that share a link from the one linking out. As a result, the page rank diminishes. The more the web pages of the site and the more links of that pages gets, the more likely that the page rank distribution of each page would be lower. The one that is distributed is not necessarily the “page rank.” What I am really talking about is the link juice. The link juice is passed to all the web pages of the site which if kept added would boost the page rank of a certain web page.

However, SEO experts themselves negates that the determining factor of getting ranked higher in the SERP is not just page rank. It is more on the uniqueness of the content of each web page and the relevance of keywords and the links that you generate out of link building, either internal or external linking.