Vaughan's poem is about how hurtful words linger long after they've been said. It begins with a quick list of the damage people do with language: lies, judgments, misunderstandings, hateful speeches. The speaker calls these "words in the dark," as if they drift around unseen, like birds, until they settle into memory.
From there the poem follows what happens inside us. Feelings twist into grudges and doubts, then turn into thoughts. Morning doesn't bring relief, because the light only reminds us of "yesterday's faults" and "yesterday's words." Even our dreams replay them.
The speaker sounds weary and a little warning, as though describing something they know well. The mood is heavy and quiet, with a creeping sense of being trapped. The ending widens the idea. Words can outlast the people who said them, and even the person who heard them. They don't stay in the dark, but live "in the day and the night." The poem leaves us thinking about how carefully we should speak.