These lines in Shakespeare's Sonnet 116 mean that a beloved person's body will change over time. "Rosy lips and cheeks," in other words, the beauties of youth, will fade. Time, which is personified, or depicted as person, takes a person's beauty away. Shakespeare pictures this "taking" as Time harvesting an individual's beauty just as a person harvests a ripe grain crop with a sickle. Since death is traditionally depicted as a grim reaper carrying a sickle, Shakespeare is identifying Time with death.
However, Shakespeare argues, love is not fooled by what Time takes away. Love is stronger than time. A person's outward appearance might alter over time, but love doesn't care. Time doesn't matter to love, which will endure even past death, to the point of doomsday, the last day of the world's existence.