What is the significance of the combination of Sri Krishna and Arjuna ?
Man needs the combination, in his character, of yoga, or the transcendental vision of Krishna, and the Promethean fire of Arjuna. In the Mahabharata war, Krishna did not do any fighting, he was only the unarmed charioteer of Arjuna. Arjuna was the fighter, the man of action, in the battlefield. But that action of Arjuna had the strength of Krishna's vision behind it. That made it not the blind, self-cancelling, inefficient action of the ego, but the steady, purposeful, and efficient action of the illumined mind, of the बुद्धि (buddhi).
Action becomes a snare and a defeat for man when it does not draw nourishment from his true Self, which is the Self of all. Action illumined by the knowledge of the Self becomes itself illumination, and ceases to be mere action. Work becomes worship. All true action finds its consummation in illumination, says the Gita (IV. 33). This combination of vision and action is what the Gita teaches, through which man achieves a double efficiency, namely, practical efficiency by which he becomes a productive unit of society and enhances its life and welfare, and spiritual, inward, efficiency by which he achieves the awareness of his immortal divine nature.
Reference: The Message of the Upanishads by Swami Ranganathananda (p.149)