When I have fears that I may cease to be
Before my pen has glean'd my teeming brain,
Before high piled books, in charact'ry,
Hold like rich garners the full-ripen'd grain;
When I behold, upon the night's starr'd face,
Huge cloudy symbols of a high romance,
And think that I may never live to trace
Their shadows, with the magic hand of chance;
And when I feel, fair creature of an hour!
The speaker’s deepest and most ambitious visions come to him in his quiet moments of reflection. He finds a vast amount of inspiration in the cosmos, with the night’s stars and clouds reminding him of the limited time he has left in the world to express all of his burning thoughts. 
 The line mixes the senses, ‘huge cloudy’ symbols used to describe emotional, romantic stories, an example of  synaesthesia .