Yeats starts the poem off by talking about the dudes he runs into in the street when the shops and offices are closing up around Dublin. He basically makes superficial small talk with them, saying "polite meaningless words" (6). And every now and then, he'll tell a funny story that might get a laugh at the bar. But he doesn't really value his interactions with any of these people. So yeah—dude's a bit of a snooty jerk.
Next, Yeats breaks off and starts going through a list of all the people who were involved with the Easter Uprising of 1916. He mentions a woman who helped out with the effort, along with some other guys who might have had bright futures if they hadn't gotten themselves executed for treason. One guy was even responsible for hurting people close to Yeats, and Yeats didn't think much of him. But still, Yeats is getting a little uncertain about his superiority, and is starting to wonder if these people he's mentioning might actually be heroes.
As he continues, Yeats compares these fighters and their unchanging dedication to a rock that sitting at the bottom of a stream. The stream and the nature around it keep changing, but the stone remains unmoved. At the end of the day, Yeats isn't sure how much he admires the people he's talking about. But he definitely has learned to respect them and the sacrifice they made for something they believed in.
Yeats closes the poem by repeating the phrase "A terrible beauty is born," which he's mentioned several times in the poem. Basically, this phrase closes the poem by suggesting that even though the deaths of the Easter Uprising are terrible, history tends to remember bloody battles and self-sacrifice more than anything else. So with regards to being remembered, there's kind of a terrible beauty in the death that came out of Easter, 1916.