The diction in the poem is elevated and formal, with a consistent use of metaphorical language. For example, in the first quatrain, the speaker refers to his love as "a summer's day," and in the second quatrain, he compares her eyes to "two stars." The poem also contains several examples of personification, such as the use of "Death" as a character.
In addition to its rich use of figurative language, the poem is also characterized by a complex syntax that often involves the use of enjambment. For example, in the first quatrain, the speaker's sentence about how his love is "more temperate" than a summer day continues into the second line, creating a smooth flow of language. The use of enjambment throughout the poem helps to create a sense of urgency and passion.
Overall, the diction and syntax of Sonnet 29 are both essential to the poem's meaning and impact. The elevated language and complex sentence structures help to create a sense of timelessness and importance, and the use of figurative language and enjambment contributes to the poem's emotional intensity.