Here is a more detailed explanation of the meaning of the poem:
Stanza 1:
The speaker begins by asking if he should compare the beloved to a summer day. He then lists several characteristics of a summer day: it is beautiful, pleasant, and full of life.
Stanza 2:
The speaker continues to praise the summer day. He says that it is "temperate" (meaning moderate and gentle), and that its beauty is "more lasting than the painted flowers."
Stanza 3:
The speaker then compares the beloved to the summer day. He says that the beloved's beauty is "more lovely and more temperate" than a summer day.
Stanza 4:
The speaker concludes the poem by saying that the beloved's beauty will "never fade nor lose your heavenly light." This is a reference to the fact that the beloved's beauty is not just physical beauty, but also spiritual beauty. The beloved's beauty is something that will last forever, even after the summer day is gone.
The overall meaning of the poem is that the speaker is expressing his deep love and admiration for the beloved. He believes that the beloved's beauty is surpassing anything else in the world. The beloved's beauty is something that will last forever, and it will never fade.