RALPH:  Macbeth compares a Scotland without Duncan to an empty wine barrel. The dregs are the leftovers in the bottom of the barrel after the good wine has been drained off.

DAVINA:  Shakespeare also makes a pun on the word “vault.” A vault is an arched roof, such as you would find in a wine cellar. But it also refers to Duncan’s burial vault. And finally, it metaphorically represents the sky over Scotland, which now looks down on the kingdom and can find no one worth bragging about since Duncan is gone.