Answer:
The tone of the poem changes in the last two lines.
Step-by-step explanation:
The given excerpt is taken from Sonnet 17, written by William Shakespeare. The sonnet is the last of the 'Procreation sonnet.' Through the medium of sonnets, the Sonneteer is trying to persuade the Fair Youth to marry him and procreate a child with him.
The Sonneteer is concerned that the poems that he has written describing the beauty of the Fair Youth, will be considered false by readers. Therefore, he persuades the Fair Youth to birth his child, who will testify on his behalf in the future.
This shift in the tone is seen in the last two lines of the sonnet.