Analysis of But Most Thy Light

I know how fire burns,
How from the wrangling fumes
Rose and amber blooms,
And slowly dies.

Nothing's so swift as fire,
There's nothing alive so fierce.
The lifted lances pierce,
Sink, and upspring.

Like an Indian sword it leaps
Out of the smoking sheath.
Even the winged feet of death
Learn speed from fire;

And pain its cunning learns;
Languor its sweet
From the decaying heat
That never dies.

I know how fire burns
Unguessed, save for tears,
When the thousand-fanged flame spears
The body's guard;

Or when the mind, the mind
Is ever-glowing wood,
And fire runs in the blood
Lunatic, blind;

When remorse burns and burns
And burns always, always--
The fire that surest slays
Or surest numbs.

I know how fire burns
But how I cannot tell.
And Heaven burns like Hell
Yet the Heart endures.

'Tis the immortal Flame
In mortal life that's bitter,
Or than all sweet sweeter
Though life burns down.

Teach me, fire, but this,
Nor alone destroying burn:--
Of thy warmth let me learn,
But most thy light.