What is the purpose of these lines? to complain about the intense heat and humidity of summer
to persuade a loved one to visit during a warm season
to express love by likening a loved one to a nice day
to argue that hot weather is more pleasant than cold weather

Here are the lines:  Shall I compare thee to a summer's day? Thou art more lovely and more temperate: Rough winds do shake the darling buds of May, And summer's lease hath all too short a date

to express love by likening a loved one to a nice day

Explanation:

Comparisons are most times used in literature to help people have better visualization and appreciation of a subject being discussed by a speaker. In these lines from Shakespeare's Sonnet 18, he likens his loved one to a summer's day. Just as a summer day was bright and temperate, so was his lover lovely and gentle. He also likens his lover to a beautiful bud that remained unshaken despite the unfavorable winds.

the correct answer is:

this is an example of the writer telling through description rather than showing through dialogue.

sometimes writers like to explain explicitely what's happening instead of adding dialogues of the situations., which is the case in this passage,

dr. kings dream speech

explanation:

it was late in the day and hot, and after a long march and an afternoon of speeches about federal legislation, unemployment and racial and social justice, the rev. dr. martin luther king jr. finally stepped to the lectern, in front of the lincoln memorial, to address the crowd of 250,000 gathered on the national mall.