Krishna talks to Arjuna about Karma yoga, and stresses that one should do one’s duty, without being attached to the results of such action. But how can anyone be motivated to do anything, if he is not to think of the results? That becomes possible, if a person realises that God is the One who makes him do his karma.
There are many police personnel, and they all may be armed, but unless the shooting order comes from an officer in a high post, those lower down will not fire. Likewise is the position of every human being. The senses he has are akin to the weapons of the policemen. And just as policemen use their weapons, when it is their duty to, we should use our senses to perform those actions that are required of us. The spies of a king gather information about enemy kings, only because their king tells them to. Likewise, we do our karma, because the Lord makes us do them, said Valayapet Ramachariar, in a discourse.
If we act in this spirit, then we will no longer be attached to the results. Now Arjuna has a doubt. If God makes us do everything, then can He blamed for our sins? The Lord answers this question too. He has given us a set of rules — speak the truth, speak kind words, honour your parents, treat guests with respect etc. Nowhere does He tell us to sin. Given the rules, if we still go astray, then He cannot be blamed. But when we act within the framework of rules, there is no need for us to worry about the result. In fact we should not think of the results. If we do our karma in this spirit, then we get purified, and can proceed to bhakti yoga.