Bright star! would I were steadfast as thou art—
Not in lone splendour hung aloft the night,
And watching, with eternal lids apart,
Like Nature's patient, sleepless Eremite,
The moving waters at their priestlike task
Of pure ablution round earth's human shores,
Or gazing on the new soft fallen mask
Of snow upon the mountains and the moors—
No—yet still steadfast, still unchangeable,
Pillow'd upon my fair love's ripening breast,
To feel for ever its soft fall and swell,
Awake for ever in a sweet unrest,
At the  volta  there is a firm ‘no’ followed by a second dash, another  caesura . This line is important, on which the poem pivots.  The repetition of ‘still’ gives further emphasis. 
 The ‘No’ is the point where a new direction is taken in the reasoning. The reference to the cosmos, the ‘steadfast’ and unchanging natural world is for the moment dismissed. The poet doesn’t think he can be as steadfast as the star — and yet he is, in terms of his devotion to ‘my fair love’. It’s the moment where the star, is related to his own human life.