Read the stanza from Shakespeare's "Sonnet 18." 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: What is the purpose of these lines?

If we are going to analyze the given lines above from the stanza from Shakespeare’s "Sonnet 18," the purpose of the following lines is that the poet attempts to compare it to a summer's day, but shows that there can be no such comparison, since the fair lord's timeless beauty far surpasses that of the fleeting, inconstant season. Hope this answers your question.