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2. Time will affect the beauty of this person negatively. It will destroy the beauty.
3. The young person will defeat time by having his name forever remembered through Shaespeare's literature. The poem spends the first 3 quatrains saying how the persons beauty will fade and dissappear with time. Then, with a twist on what is expected, it says that the person will be remembered forever through a poem that doesn't even have his name. It's like a slap to the face.
4. That beauty doesn't last forever. Enjoy it now, because time will destroy it.