What are most closely the central themes of Sonnet 18?

The central themes of Sonnet 18, written by William Shakespeare, can be summarized as follows:

1. The immortality of poetry: The poem explores the idea that through his verses, the poet can preserve the beauty of the Fair Youth (the intended recipient of the sonnet) for eternity. It suggests that poetry has the power to defy the ravages of time and keep the beloved's beauty alive.

2. The transient nature of life: A recurring theme in the sonnet is the idea that everything in life is fleeting. The first quatrain emphasizes the transience of summer and its beauty, while the second quatrain compares the beloved's beauty to that of a summer's day, highlighting their impermanence.

3. The power of poetry: The poem showcases the power of language and poetry to immortalize moments and emotions. It suggests that the poet's words are eternal and will ensure that the Fair Youth's beauty remains alive and celebrated in future generations.

4. The enduring qualities of love: Shakespeare expresses profound love and admiration for the Fair Youth. The sonnet portrays love as a force that transcends time and physical beauty. The final couplet declares that as long as people read the poem, the Youth's beauty and their love will continue to thrive.

In summary, the central themes of Sonnet 18 are the immortality of poetry, the transient nature of life, the power of poetry, and the enduring qualities of love.