We may say that the idea of good and bad is itself part of His grand plan. However hard we may intellectualise that there is no good and bad, yet we do not act according to our conceptions but as our nature drives us. Even the urge to do good is also arising out of prakriti just as the urge to evil. The teaching indeed draws a distinction between good and evil, deva and asura, as also the three gunas of nature that determine the value of all our actions. What it does however take away is the extreme sense of self-importance that we give to our ego-self that is itself a temporary construct of nature. It is like a film whose script is already written, the actors for each particular role already chosen according to the level of their evolution. The result is also already predetermined.
What then is our role if any, we may ask. According to the Gita, as long as we remain subject to the play of nature as indeed most are, there is very little role so to say. Yet we are not born to remain forever subject to this play of nature. We can be truly free if we discover our oneness with the Lord. The difference then is that we become conscious participants in the play. We then do what we are called upon to do with perfection, in a state of peace and joy that comes when we are freed from the sense of the ego and responsibility or harassed constantly with the sense of dualities of good and bad, success and failure, victory and defeat, joy and sorrow. We remain unattached to the outcome but fully surrendered in the action. Action is done through us according to the Will of the Lord as determined by the gunas of nature. As for ourselves we remain inwardly one with Him and let things develop as the Lord deems fit.