What is the theme of sonnet 63?

The theme of Sonnet 63 is the fleeting nature of time and beauty, and the power of love to transcend these limitations. The sonnet begins by acknowledging the passage of time and the fading of beauty, comparing the speaker's beloved to a summer's day that is cut short by winter. However, the speaker then argues that love is stronger than time and death, and that it can preserve beauty and youth in the face of these forces. The sonnet concludes with the speaker expressing his hope that his love for his beloved will endure forever, even beyond death.