"Elegy in a Country Churchyard" has a kind of hushed, quiet sound to it, with a regular rhyme and rhythm—almost like the ticking of a quiet clock. The hush-hush quality to the poem seems appropriate, given both the subject (death!) and the setting (a graveyard in a country churchyard!). Let's look at an example in the second stanza:
Now fades the glimm'ring landscape on the sight,
And all the air a solemn stillness holds,
Save where the beetle wheels his droning flight,
And drowsy tinklings lull the distant folds; (5-8)
The repeated S and Z sounds in this stanza represent what's called in the poetry biz consonance. The effect is a kind of shh-shh, hushing sound—almost as though the speaker were subtly asking us to lower our voices so that we could hear the wind in the trees and the call of the owl in the tower. And, of course, so that we can listen to his poem.
The regularity of the rhythm (check out the "Form and Meter" section for more deets on that!) helps to remind us of the passage of time, which seems appropriate, since the poem is about how people are remembered after they die. And the tick-tock-tick-tock regularity of the poem reminds us that our own lives are passing right now. Tick-tock!