Why does Hume emphasize this distinction?

1.To underscore the limits of what Reason can know: All that Reason can do is assent to logical or mathematical truths. Reason can tell us nothing about “matters of fact,” i.e., about what the world is really like.
2.Hume says that anything we think we do know about the world, can only be based on experience. We can have no knowledge of what the world is like... apart from experience.
3.But then again: that “knowledge of the world” is derived from our impressions. We have no knowledge of anything beyond our impressions/ideas!