The reward of an action when we understand it properly is not anything different from the action itself. An action done in the PRESENT when is conditioned by a FUTURE-time appears as the fruit-of-action.
In fact, the action ends or fulfils itself only in its reaction, and the reaction is not anything different from the action. An action performed in the present when defined in terms of a future moment is its reaction. Therefore, to worry over and get ourselves preoccupied with
the anxieties for the rewards of actions is to escape from the dynamic PRESENT moment and live in a FUTURE moment that is not yet born!
In short, the Lord’s advice here is a call to man not to waste his present moment in fruitless dreams and fears, but to bring out his best, all of the best from within him, to the PRESENT moment, and vitally live every moment. The promise is that the future shall take care of itself, and shall provide the Karma Yogin with the achievements that are divine and accomplishments that are supreme.