Because it's not one to pass up. The Shade #4 is written by James Robinson at his Starman best (it's even a tale of Times Past, the popular done-in-one interludes from the ongoing arcs); pencilled by New Frontier's Darwyn Cooke; inked by the extremely talented J Bone; features The Shade's first foray into fighting the Nazis as he finally acknowledges the family he left behind decades previously; includes spies, turncoats and not one, but two guest stars from the dawn of superhero comics; and it feeds back into this splendid maxi-series' ongoing plotline.
From the wry opening lines ('It was April 14, 1944. And I confess, until that day my only anti-German act had been abstaining from pumpernickel') to a touching close, this is just a wonderful story. It uses DC's rich family history, without demanding any familiarity from the reader. So while it may enrich your experience to note that a plotline originating in a 1940 Quality Comics strip is finally tied up, if you don't know, the detail works simply as a coda to one character's story.
Robinson also lets us get to know the Shade a little better, shining light not just on his attitude to patriotism, but on the knave's identity he has constructed for himself. His descendant, Caldecott, manages to come across as a truly good man without seeming in the least sanctimonious. And as a snapshot of America during the Second World War, the script works a treat.
Whether or not you followed the Starman series which hosted Robinson's reinvention of the Shade, even if you've not read the first three issues of this series (and you should), I urge you to give this one-off a try. It's simply a fine comic story.