Republishing versus updating blog posts

Hey!

I've been reading a lot about republishing/refreshing/updating old blog posts to gain more traction.

However - I can't find anything specifying if that means updating the content (i.e. saving your changes in your CMS) or updating the content AND updating the publish date.

Does publish date even matter if people are finding the article in SERPs rather than on our blog page? (Like, I don't need them to see the article at the top of our blog page because most of our article traffic is directly to that post from the SERP).