The essence of karma

Is there any destiny,is our mind slave to the circumstances.What we are doing as usually in our life,why Lord krishna says in bhagwat Gita "karmanye vaadikarste ma fleshukadachin" does this means that we are helpless somewhere? why Lord krishna says "You have the right to do karma and the fruits of this is not in your hand, fruits are in the hands of vidhata,vidhata means controlling power,is there any controlling power or we can say our karma is really a controlling power,does this perplex us? All the ancient holy scriptures and great saints teach us to lead a simple life and do karma with full devotion,this is the real essence of karma that means do your karma with full devotion and go away from all the affectation ,if you do this the failures can not distrub you.Actually the planets who control us,are also not free they are also bound to do their karma,as some people say Lord has the full control over stars and on us.The matter of fact is that some power is present in this cosmos but that power does not interfere in karma cycle,that power believes in karma theory and are also bound to do it,you take the example from our holy scriptures that all the great saints and avtaras had the full capacity to do all the things or to do miracles but they never interfere with the karma theory or never brake any rules which have been made for this universe,you take the example of Sun who never crossed his limit and since the existence of this universe he is doing his job with full devotion and with punctuallity,actually we are all bound to do karma and we are all responsible for our karma.We have the free will except somewhere and we have to do all the things but do it with balanced mind,what you do that will pay you in that way it is sure,so always do good karma and always listen to your soul.