Explanation: Being certain that they and I But lived where motley is worn: All changed, changed utterly: A terrible beauty is born.

  The speaker had nothing more serious on his mind than a joke because he thought that they all were just living regular, unimportant lives. Now, though, everything is completely, totally different. Some events have occurred that were highly destructive but also helped bring about profound change. Easter Rising has changed everything. The speaker acknowledges that Irish history will be forever transformed by the event of Easter Rising. A terrible beauty is born is an oxymoron. Terrible and beauty are opposite sentiments and speak about the concept of the sublime in which horror and beauty can exist simultaneously. The Easter Rising was terrible because of its violence and loss of life, but the beauty was in the dream of independence.