The 'eternal lines' are the writings of the poet Here it refers to the present sonnet................

SHALL I COMPARE THEE TO A SUMMER'S DAY

When in eternal lines to time thou grow'st- What are 'eternal lines' ? Who is the poet addressed to ? How will 'thou grow'st in eternal lines?

* The 'eternal lines' are the writings of the poet Here it refers to the present sonnet.

* Here the poet's beloved friend is addressed to. He is a rich young nobleman. whom the poet I loves and trusts.

*Shakespeare is conscious of his strength of poetic faculty. He is sure that his poetry will be enjoyed by future generations. He sings of the glory and grace of his beloved friend in his poet. Obviously his readers will read his poetry and admire his friend. They will keep the image of his handsome friend in their minds as an object of beauty. In this way the poet's friend will be immortalized.