Consciousness prefers the passive, the weak--the "feminine."
Detached restraint is the best policy.
Joyful events celebrate the feminine;
Victory in battle is, therefore, an opportunity for mourning, and should be treated as one.
Secondly, this verse talks a lot about left and right, feminine and masculine. These are references to Yin and Yang, not "women" and "men" per se. Here's what it says about this polarity: consciousness requires a yin state of mind, whether it be your own personal unit of consciousness or the Universal Unit of Consciousness with which your personal UC longs to be united. To be or become conscious, one must cultivate and dwell in the passive, feminine, yin state; which is to say, "receptive."
|The rising yang is the white area on the left.|
The sinking yin is the black area on the right.
Lastly, here's how I interpret the part about the second-in-command occupying the yang position and the commander occupying the yin position: when seeking enlightenment, or alignment with the Universal UC or God's will, your personal UC needs to hold the commander's position in your soul. If your UC is in control, rather than your "little me" mind or your emotional yang passions, you will be in the passive, yin state and able to channel the Universal UC. In that state, it is just fine for the passions and mind to be second-in-command; this is how it should be. When those roles are reversed, as they are for most people whose theatre of action is in the material world, their yang state precludes the receptivity required for enlightenment. Therefore, when, with full consciousness of the tragic consequences, the UC must preside over war, this is an occasion for mourning, as if presiding over a funeral.