How to display featured images in latest posts list (grid) with twenty seventeen

Using Twenty-seventeen, I would like to display the featured images of each post appearing in my latest posts grid. (The URL indicated here links to a sandbox page. I am trying to get the sandbox to look like the actual homepage without the use of BeaverBuilder plugin). I don’t understand why the theme doesn’t do that by default.

The page I need help with: [log in to see the link]