Why external link is important for a SEO?

External link is very important from the point of view of SEO. Backlink is one of the important factor in Google's Ranking Factor. If we get External Link from any other website, then in the view of Google our website has Authority Increase. This gives a direct signal to Google that the content of our website is valuable. Similarly, when we give External Link to another High Authority website, Google builds trust on that website as well as our website.