The boast of heraldry, the pomp of pow'r, And all that beauty, all that wealth e'er gave, Awaits alike th' inevitable hour. The paths of glory lead but to the grave.
Aha. Here's the real reason why the speaker doesn't want proud, ambitious, grand people to make fun of the poor people in the churchyard: it's because we're all heading there someday, too!
Here are a few nitty-gritty vocab notes before we start unraveling the sentence structure of these lines: "Heraldry" is the coat of arms associated with old, aristocratic families. Families with a coat of arms would embroider it on everything from their servants' coats to the outside of their carriage to the screen in front of the fireplace. Check out this example.
"Pomp" means proud, meaningless ceremony—basically, any ceremony designed to make people feel important but that doesn't really convey any meaning.
Last one: "inevitable" means unavoidable.
Phew. Okay. Now let's get back to the summary! The speaker starts with a list (this guy seems to be fond of lists). Here we go: 1) Bragging about your family's heraldry, 2) The empty ceremony of being in a position of power, and 3) The beauty that can be obtained from wealth—all of those things are waiting for the unavoidable, inevitable time.
What time, you ask? Yep, you guessed it: all of those paths lead only to the GRAVE.