Okay, "Elegy Written in a Country Churchyard" isn't just about death. We promised some less-depressing themes, and this is one of them: the poem is about how we're remembered after we're gone. That's not so bad, is it? What's that? Still don't like thinking about the whole "after you're gone" part? Well, fine—this one's a bit depressing, too.
Statues shmatues! In this poem, the speaker wants to emphasize the importance of lives that are not commemorated by monuments or remembered by official history: the lives of common people that could potentially have been Miltons or Cromwells, if only they had been recognized and remembered.
Thomas Gray suggests that death is democratizing—it strikes down rich people as well as poor people—but he goes further to suggest that we might be remembering the wrong people for the wrong things. Food for thought, gang.