That line comes from a long Wordsworth poem titled “The Excursion”. I quote a portion here.
[begin quote:]
I have seen
A curious Child, who dwelt upon a tract
Of inland ground, applying to his ear
The convolutions of a smooth-lipped Shell;
To which, in silence hushed, his very soul
Listened intensely; and his countenance soon
Brightened with joy; for murmurings from within
Were heard,—sonorous cadences! whereby,
To his belief, the Monitor expressed
Mysterious union with its native Sea.
Even such a Shell the Universe itself
Is to the ear of Faith; and there are times,
I doubt not, when to You it doth impart
Authentic tidings of invisible things;
Of ebb and flow, and ever-during power;
And central peace, subsisting at the heart
Of endless agitation.
[end]