What does this philosophical piece of writing about immortality mean?

“The Don Juan in Hell joke, that heaven’s prospects are tedious and that the devil has the best tunes, though a tired fancy in itself, at least serves to show up a real and (I suspect) a profound difficulty, of providing any model of an unending, supposedly satisfying, state or activity which would not rightly prove boring to anyone who remained conscious of himself and who had acquired a character, interests, tastes and impatiences in the course of life already, a finite life. The point is not that for such a man boredom would be a tiresome consequence of the supposed states or activities, and that they would be objectionable just on the utilitarian or hedonistic ground that they had this disagreeable feature. If that were all there was to it, we could imagine the feature away, along no doubt with other disagreeable features of human life in its present imperfection. The point is rather that boredom, as sometimes in more ordinary cirstances, would be not just a tiresome effect, but a reaction almost perceptual in character to the poverty of one’s relation to the environment. Nothing less will do for eternity than something that makes boredom unthinkable. What could that be? Something that could be guaranteed to be at every moment utterly absorbing? But if a man has and retains a character, there is no reason to suppose that there is anything that could be that. If, lacking a conception of the guaranteedly absorbing activity, one tries merely to think away the reaction of boredom, one is no longer supposing an improvement in the cirstances, but merely an impoverishment in his consciousness of them. Just as being bored can be a sign of not noticing, understanding or appreciating enough, so equally not being bored can be a sign of not noticing, or not reflecting, enough.” (B. Williams, “The Makropulos Case: Reflections on the Tedium of Immortality” in his Problems of the Self, pp. 94-5)