Let us say that there are two ways of defeating the evil that is ingrained in the reality of our lives.
One is by choking its growth, not allowing it nourishment, isolating it from all contact, as in the Garden of Eden.
The other way is the far more complicated way of struggle after the evil has been released into the Garden.
Once the evil has spread, then death works its inevitable havoc.
The spirit of evil is not so easily removed from the earth after man knows sin.
Great struggles, long-lived, involved, and desperate, characterize man's history.
An ancient analogy provides a graphic description.
A garden is surrounded by a fence and the evil beasts are outside.
Man's job is to watch over the garden and to patrol the fence so the wild beasts do not enter.
But once the fence is broken and the evil penetrates, his task is to fight the beasts, both those already in the garden and those outside trying to enter.
Were the man permitted to make his escape, the garden would be abandoned and go to ruin.
Hence man is not so easily allowed to get out of his responsibility.
He has to stay on earth, continue to care for the garden, and try to get rid of the evil he has himself introduced.
–Rabbi Adin Steinsaltz
From In the Beginning by Rabbi Adin Steinsaltz