The speaker opens with a dramatic sigh—“Alack!”—frustrated that his poetic gift feels so meager. He believes the beloved he’s trying to honour is already far more valuable in its bare, unadorned state than when he adds his own flattery. He asks not to be blamed if he stops writing: just look into a mirror, and that reflection will completely overpower his clumsy pen, making his lines seem dull and almost shameful.
Trying to improve on such natural perfection strikes him as sinful—why risk spoiling what is already flawless? His verses can only point toward the beloved’s graces, but the closing couplet admits a gentle defeat: the mirror reveals “more, much more” than any sonnet can contain. The mood is affectionate and wryly self-mocking, full of an awe that words can’t quite reach.