In "Shall I Compare Thee" Shakespeare first proposes to compare his friend's beauty to that of a summer's day, because both are bright and beautiful in appearence. The sunny day and the golden complexion of the friend have a great kinship. But he hesitates, and finally finds it in an unsatisfactory comparison because his friend's beauty is steady and permanent, while that of a summer's day in uncertain and temporary.

            In summer, sometimes the sun is too hot, and sometimes it is dimmed by clouds. The wind at times blows too fiercely, making the buds and young flowers very uncomfortable. All beautiful things and persons lose their beauty in course of time. There is a pun on the word 'fair' in this line. The first 'fair' means 'fair person or thing', and second 'fair' means the state or condition of the highest perfection, when that person or thing is at the peak of beauty. Every beautiful creature and thing must become unattractive in course of time. The change for the worse  may take place in two ways, either suddenly, due to an accident; or gradually, according to the inevitable law of nature.

         The summer of Nature has a short span of life; it has to give way to autumn. But the summer like beauty of poet's friend shall not fade and it will be preserved forever through the poet's immortal poetry.Though death rules over the world, and all human beings lose their lives, and go to the shadowy world of death,  the poet's friend will never die.The 'eternal lines' means the poetry of the poet, Shakespeare. It will live forever on earth. The friend grows eternally because as time goes more and more readers will appreciate his beautiful image, recorded in the poet's sonnets.

        Through the couplet the poet wants to immortalize his friend's beauty. He said that his poetry will make him immortal. So long as men live on earth and can read poetry, this sonnet will give immortality to his beautiful young friend who is "world's fresh ornament". 

This line have been taken from 'Shall I Compare Thee' written by William Shakespeare. The poet here strongly advocated for the perpetual continuity of his friend's beauty.

      The 'eternal summer' of Shakespeare's supposed patron-friend W.H. is referred to here. In these lines the poet powerfully told that unlike the beauty of summer's day, his friend's beauty is eternal and perpetual. It is too endurable to fade. It wiil not vanish by the destructive march of time. The poet here boldly affirms that his friend is the embodiment of eternal beauty. His loveliness frowns at death even. The poet wants to immortalize his friend's beauty through his verse. As long as his verse will last, his friend's beauty will last. Nothing can steal away his summer nor defile the sublimity that his friend is possessed of. The enduring effect of his poetry will ennoble his friend with everlastingness.