The speaker begins on an ordinary morning, yet talks about death, and immediately complicates it: they say they don't believe in mourning. There's a tone of weary honesty here. Growing old has left them so worn down that they feel "ashamed / to be in the picture," as if they've outstayed their welcome, or don't want to be looked at.
The ending shifts suddenly. A "she" appears and shows the group her cabinet of "very pretty prayers." The line is gentle, a little odd, and open to more than one reading. The prayers might be sincere comfort, or they might seem decorative, like objects kept on a shelf. The speaker's skepticism about mourning sits beside her tidy, beautiful faith. The title, "Matins," a word for morning prayer, adds to this. The mood is quiet, wry, and uneasy, with tenderness and doubt held side by side.