How would you analyze Line 8 of John Updike's "Perfection Wasted"?
And another regrettable thing about death
is the ceasing of your own brand of magic,
which took a whole life to develop and market —
the quips, the witticisms, the slant
adjusted to a few, those loved ones nearest
the lip of the stage, their soft faces blanched
in the footlight glow, their laughter close to tears,
their tears confused with their diamond earrings,
their warm pooled breath in and out with your heartbeat,
their response and your performance twinned.
The jokes over the phone. The memories packed
in the rapid-access file. The whole act.
Who will do it again? That's it: no one;
imitators and descendants aren't the same.
This excellent poem concerns the theme of death, and, building on this theme, the irreplaceable tragedy it is when one human dies and how their "perfection" is "wasted" as when they die, their uniqueness disappears forever. The very clever and novel way that Updike presents this theme is by thinking about the "brand of magic" of each person--their own witticisms and sense of humour. He then imagines life as if it were a stand up comedy show, with our nearest and dearest closest to the performance. This extended metaphor encompasses line 8, which you have asked for an analysis of. This is part of the "show," as the speaker is unable to distinguish between the diamond earrings and the tears of his audience. The reference to tears shows how closely comedy is linked to pain and suffering, and the grief that we all experience when someone dies. Comedy and grief seem to be contradictory states that are not that far apart after all.
We can answer only one question at a time; so I've edited your question to the analysis of Line 8. As the poem's speaker--someone who has either experienced the death of someone close to him recently or who is at an age when death seems near--ponders death, he considers how no one else on the planet has the same connection as he does with his close family or friends. He enjoys that they allow him to be himself, in a sense performing for them, that they allow him to be the life of the party, cracking inside jokes and basking in the rapport that they all share.
Keeping that unique relationship in mind as you read the poem, consider then the similarities between the glistening of tears and the sparkling of diamonds. From a literal standpoint, after bringing his friends to tears with laughter from his quick wit, the speaker looks at his "audience" and sees the glistening from their tears and earrings. In the context of the poem, though, the figurative connection between tears and diamonds is more significant. Both tears and diamonds are obviously precious to most humans. For the speaker, the tears of laughter are so precious because they illustrate the unique personal bond that he has with those whom he has brought to tears, and of course, diamonds are the most precious of stones. Updike implies that kinship with others (represented by the tears) is as valuable or perhaps more valuable than tangible objects (such as diamonds).