The theme of this sonnet is actually a theme that concerns many of Shakespeare's sonnets: that of the immortality of his beloved in the face of time and the way that commemorating his beloved's beauty in verse creates that immortality. Note the way that the first two lines indicate this by stating clearly that no "gilded monuments" or statues of marble can "outlive this powerful rhyme." Statues and such monuments that are created to commemorate the lives of famous people are fated to be destroyed and to be "besmear'd with slutting time." However, the monument that Shakespeare erects to his beloved in the form of this poem is untouchable:
Nor Mars his sword nor war's quick fire shall burn
The living record of your memory.
Thus this poem will allow the speaker's beloved to "pace forth" against death and oblivion until the end of "this world" and judgement day. The last couplet cements this overall theme of immortality through art:
So, till the judgment that yourself arise,
You live in this, and dwell in lovers' eyes.
Shakespeare thus has given the gift of eternal life to his beloved through giving him life "in this," the poem that we read today, signifying the truth of his words.