"The Tide Rises, the Tide Falls" is a sad and somber poem about the inevitability of death. The first two stanzas are all about the falling of the tide, darkness and twilight descending, and the death of a nondescript traveler. There is nothing heartwarming or uplifting about this whatsoever. To add insult to injury, the speaker uses a lot of long vowels in the first stanzas. There's the long I in "tide," "twilight," "rises," and "white"; the long A in "waves," "hastens," and "efface"; and the long E in "sea." Long vowels can often make something sound more depressing and sad, and that is exactly what they do in the poem's first stanzas.
Now even though this poem has a lot of long vowels that make us feel really depressed, it also has a lot of repetition to offset that depressing feeling (we'll explain how repetition does that in just a second here). But first, let's talk about what kind of repetition there is. Right off the bat, we get the title: "The Tide Rises, the Tide Falls." Did you notice how the long I sound is repeated in both "tide" and "rises"? Did you notice how the final word in each part of the title ends in S? In addition, there's the refrain, which we see in lines 1, 5, 10, and 15. Then there's a whole bunch of alliteration on top of that (the T's of the refrain, the W's in line 8, the S's in lines 11-12). On top of that, there are a number of words that just keep showing up ("sea" appears three times, as does some form of the word "dark").
Okay, cool, lots of repetition—but what does it all mean? Think of it like this. This is a poem about death, but it's also a poem about life and life cycles. Tides rise and fall and rise again. People are born, live, and die, but then other people are born, live, and die. In the same way that sounds and phrases keep showing up, so too does life continue to flourish, even death though is a lamentable and ever-present reality.