William Shakespeare's "Sonnet 97" is part of the Fair Youth sequence in which "the poet expresses his love towards a young man."
The metaphorical comparison between the speaker's love and his (assumed gender based upon the universal idea that Shakespeare's sonnets were his experiences) lover are illustrated through the use of winter.
In the sonnet, the speaker's time away from his love feels like winter (dry, empty, and cold). The comparison to winter speaks to the lack of life, warmth and promise of what may come (as seen with spring and summer). The speaker states that it cannot be summer if his lover is not with him (metaphorically). Essentially, the speaker feels as if the entire world has become dead: birds will not, or cannot sing, the leaves have no color and no pleasure can be found visually.
Essentially, the speaker feels dead inside, much like the world is when winter has come.