The answer is: To emphasize the horror of what has happened.
Silent Spring is an environmental book written by Rachel Carson in 1962. She focused her attention on environmental problems specially the ones caused by synthetic pesticides. Carlson wrote the book after researching to make American people aware of the problems they were facing. Even though it had opposition from the chemical companies, it brought about important changes.
In this sentence it means that the mysteries had not been solved yet or that they had not been answered yet
The speaker is saying that you need to lift up out of the depression that you are hiding
