Not Every Day Fit For Verse

'Tis not ev'ry day that I
Fitted am to prophesy:
No, but when the spirit fills
The fantastic pannicles,
Full of fire, then I write
As the Godhead doth indite.
Thus enraged, my lines are hurl'd,
Like the Sibyl's, through the world:
Look how next the holy fire
Either slakes, or doth retire;
So the fancy cools:--till when
That brave spirit comes again.