This sonnet in Amoretti is a description of the speaker's own work: meaning the leaves (pages), lines of verse, and rhymes that constitute his verse. The poet's love is pictured holding the book, reading it, and appreciating the declaration of love contained in it.
Essentially the sonnet expresses an identity between the poet and his work. The man's verse itself becomes "happy" and is glorified by his love's touching and reading it, just as the man himself is gladdened and exalted through her. She ennobles the leaves, lines, and rhymes; she holds them in love's "soft bands" and makes a captive of them. She illuminates them with a "starry light," and they are bathed in the "sacred brooke":
Of Helicon, whence she derived is.
We thus see a reciprocity or symbiosis between the poet, represented by his work, and the woman loved by him. He has produced this work for her, but by itself it has no meaning. She grants significance and power to it, and at the same time, she possesses it. So, because an identity exists between poet and poem, in her taking possession of the latter, she is also confirming her captivation of the man and her ennobling of him.
The sonnet altogether is a chain of personifications of the inanimate writing created by the speaker. In linking himself to his poetry, the poet is also saying that his love is dependent on how the object of it, his mistress, receives and understands that poetry. Therefore his love is seemingly not unconditional:
Leaves, lines and rymes seeke her to please alone,
Whom if ye please, I care for other none.
In a more literal sense, the speaker simply wishes her to appreciate his work. But metaphorically speaking, he is his poetry, and her love of it confers that love on him as well.