There's a hint about whom this poem is written. In Lowell's The Changeling, he wrote:

I had a little daughter,
    And she was given to me
To lead me gently backward
    To the Heavenly Father's knee.

        .    .    .    .    .

She had been with us scarce a twelve-month,
    And it hardly seemed a day,
When a troop of wandering angels
    Stole my little daughter away.


She Came and Went

As a twig trembles, which a bird
    Lights on to sing, then leaves unbent,
So is my memory thrilled and stirred; --
    I only know she came and went.

As clasps some lake, by gusts unriven,
    The blue dome's measureless content,
So my soul held that moment's heaven; --
    I only know she came and went.

As, at one bound, our swift spring heaps
    The orchard's full bloom and scent,
So clove her May my wintry sleeps; --
    I only know she came and went.

An angel stood and met my gaze,
    Through the low doorway of my tent;
The tent is struck, the vision stays; --
    I only know she came and went.

O, when the room grows slowly dim,
    And life's last oil is nearly spent,
One gush of light these eyes will brim,
    Only to think she came and went.

-- James Russell Lowell