Earlier quoted context omitted.
The nukes have many roles perhaps but I think the fully developed weapons are for retaliatory strike. They are the North Korean leadership saying that if the US (or China or anyone really) tries to surgically decapitate them (like the US just did in Venezuela) then the nukes are used to take the attackers with them
Yes that's the orthodox doctrine of nuclear deterrent. To be truly effective you need a triad of land-based ICBMs, nuclear-armed submarines, and aircraft-based delivery systems so that your second-strike capability remains intact through any decapitation attempts. If you don't have the triad then you need to brandish your capability more ostentatiously, like France does with its deliberate refusal to commit to a no-f…
The core parts for MAD land-based missile silos (to soak up the enemy's missiles) and submarines (to ensure a second strike). Planes are largely a diplomatic deterrent inasmuch as they're easy to send out and easy to recall.
But Pyongyang isn't playing MAD. It's playing credible threat. And for a credible threat, you just need missiles. (On land or on subs.) The point is that you raise the stakes of e.g. a Maduro operation to risking Los Angeles.