You could determine this by just looking at the specifications for the two laptops, but I’ll throw you a bone and give you some quick reasons.
-There is a 14 inch screen in the same space as the Librem 13.
-The Librem 14 has 2 RAM slots, and therefore is able to use up to 64gb (which is massive and relatively unique among laptops) while also permitting dual channel pairings.
-The Librem 14 is a new design. This means new case and internals. This gives one reason to suspect that the hinges, feet, wireless reception, etc. are things which will see an improvement.
-The placement of the kill switches are now back above the keyboard and are not a part of the hinge itself. Speaking of switches there is an additional kill switch that none of the previous Librem laptops had.I didn’t see it being all that relevant to me, so I;m a little vague on what it was. I want to say it was switch that would not allow the bios to be overwritten, or something like that.
Hopefully that helps. The Librem 14 is slated to be an impressive laptop that lives up to Purism’s goals. It is quite an accomplishment.