All changed, changed utterly A terrible beauty is born (15-16)
Now that the Irish fighters are dead, it's safe to say that they've all been changed utterly. Even Ireland's history has been changed. But Yeats might be taking it a bit far to say that the fighters' sacrifice was beautiful, even if it's a terrible beauty. Then again, maybe he's right. Your call.
He might have won fame in the end (28)
Even though Yeats is trying to commemorate people for dying in the Easter Uprising, he can't help but wonder if one of the fighters—a fellow Irish poet—could have gone on to become famous if he hadn't gotten involved in the conflict. You almost wonder if Yeats sees a bit of himself in this younger poet. You know, apart from the fact that Yeats played it safe and went on to live a long and influential life.
He, too, has resigned his part In the casual comedy (36-37)
Even though Yeats can't stand this dude named John MacBride, he has to admit that the guy was pretty brave to give his life to the cause of Irish freedom. But Yeats can't help but make one last dig by calling the Uprising a "casual comedy." In other words, there's something sadly ridiculous about the Easter Uprising, since it didn't really accomplish anything.
Too long a sacrifice Can make a stone of the heart (57-58)
For Yeats, sacrifice can be a good thing. But too much of it can make a person's heart turn to stone. After all, there's only so much death you can handle before you start to care a little less.
Was it needless death after all? For England may keep faith (67-68)
Here, Yeats says something that would have been on the minds of many Irish people, although it wasn't something you wanted to say out loud. It turns out that Ireland was going to get its independence either way after World War I; so all of the death and sacrifice of the Easter Uprising might have actually been pointless.
Now and in time to be, Wherever green is worn (77-78)
By the end of the poem, Yeats admits that whenever people were green (Ireland's official color) in the future, they will be connected to the people who died in the Easter Uprising. It's pretty much the nicest thing Yeats can say about the fighters' sacrifice without actually saying he admires them in any way.