Sonnet 63 is about a favorite theme for sonneteers, that of poetry immortalizing beauty and love. It begins with the poet saying that in preparation for the time when "my love shall be" as old as he himself is at the time of writing, he shall immortalize him "in these black lines" and keep "my lover's life" still "green," or youthful, with "sweet love's beauty."
Sonnet 63 is in iambic pentameter with two voltas, or change in topic within the subject of the sonnet. The first 12 lines are 3 quatrains with a rhyme scheme of abab cdcd efef. The last two lines are an ending rhyming couplet with the rhyme scheme gg. This is what came to be the standard English, or Shakespearean, sonnet form. It is not in the original Petrarchan sonnet form. The voltas (i.e., thought turns) are at lines 5 and 9. At 5, he turns from Time to the journey that will cause his love's kingly "beauties" to vanish "out of sight" and steal the youthful "treasure of his spring."
At 9, he turns to protesting "Against confounding age's cruel knife," asserting his love shall be "never cut from memory." The couplet explains that "His beauty shall in these black lines be seen, / ... / and he in them still green."
That [Age] shall never cut from memory
My sweet love's beauty, though my lover's life:
His beauty shall in these black lines be seen,
And they shall live, and he in them still green.