I remember this, and why (for me) it stood as a linchpin into the mythos of the Joker.
For all his instances as Evil Incarnate, Death that Laughs and other nicknames he's earned besides the Clown Prince of Crime, there has always been that touch of the mortal man inside the Joker that keeps him from just being a plot device or tool and a real living character and true menace. Because underneath the indescribable murdering lunacy, underneath the magnificently calculating cold mobster, behind the freakish showmanship in this monster, there is still a man. And everything he does is all the more terrifying because it is a man who could be good if he wrestled with his demons hard enough. Not some supernatural imp or incarnation of murderous bedlam, but a man who can achieve such despicable deeds.
And this story also explains why Batman must fight so hard against the hell he endures. Because he has to try to save everyone, even if it is the damnation of the soul underneath the Joker. For the mere mortal who commands the night and respect of the gods who walk at his shoulder, the slimmest of miracles and possibilities is something he has to reach out for. And like Gotham City itself, even the Joker can be saved.