What does the phrase kill them with kindness mean?

It is a mission, or a quest. First, you must go find the kindness blade. It will be a long, rough journey. You will find it on the top of the tallest mountain located on the most distant island. Only the purest will be able to remove the sWord from its resting place. Only the purest will remove it, and only the purest will know how to wield it!