"Until thought is linked with purpose there is no intelligent accomplishment."
A human mind cannot remain idle. Every second lots of thought of all kind comes in our mind and goes out. If we do not have any central purpose, then all these thoughts will just go 'here and there' and no Goal will be achieved.
But if there is a central purpose in life, then thought related to that will remain in your mind and prosper.
They who have no central purpose in their life fall an easy prey to petty worries, fears, troubles and destroy their life.