the short of it:
Life must contain both halves of the paradox to occur.
The Root of Authority
It has been said of old, only those who attain unity attain self-hood… Heaven attained unity and thereby is space. Earth attained unity, and thereby it is solid. Spirit attainted unity, thereby it became mind. Valleys attainted unity, therefore rivers flow down them. All things have unity and thereby have life. [Heirs] and [sovereigns] as they attain unity become standards of conduct for the nation. And the highest unity is that which produces unity.
If heaven were not space it might crack, if earth were not solid it might bend. If spirits were not unified into mind they might vanish, if valleys were not adapted to rivers they would be parched. Everything if it were not for life would burn up. Even [heirs] and [sovereigns] if they overestimate themselves and cease to be standards will presumably fall.
Therefore nobles find their roots among the commoners; the high is always founded upon the low. The reason why [heirs] and [sovereigns] speak of themselves as orphans, inferiors and unworthy, is because they recognize that their roots run down to the common life; is it not so?
If a carriage goes to pieces it is no longer a carriage, its unity is gone. A true self-hood does not desire to be overvalued as a gem, nor to be undervalued as a mere stone.
39. Taking After the Root.
The things which from of old have obtained Unity are these:
Heaven, which by Unity is clear. Earth, which by Unity is steady. Spirits, which by Unity are spiritual. The valleys, which by Unity are full (of water). All creatures, which by Unity live. [Heirs] and [sovereigns], who by Unity rule the world. This is all the result of Unity.
Heaven, but for some source of clearness, would be in danger of rending.
Earth, but for some source of steadiness, would be in danger of tumbling in pieces.
Spirits, but for some source of spirituality, would be in danger of annihilation.
Valleys, but for some source of replenishment, would be in danger of drying up.
All creatures, but for some source of vitality, would be in danger of extinction.
[Heirs] and [sovereigns], were it not for some source of dignity and highness, would be in danger of an ignominious fall. And here (in this last case) one sees how nobility is rooted in (and entirely dependent upon) what is ignoble; and highness is founded and supported upon what is low. Hence it is that [heirs] and [sovereigns] speak of themselves as orphans, lonely [people], and wheelless carts. Is this not an acknowledgement that they are rooted in (and dependent upon) their inferiors? Deny it! Why, a cart taken in pieces is no cart. A [person] has just as much objection to be isolated like a solidarity gem, as to be lost in a crowd, like a pebble.
39. (Untitled).
These are they which from of Old have obtained Unity:
Heaven obtained Unity by purity; the earth obtained Unity by repose; Spiritual beings obtained Unity by lack of bodily form; The valleys obtained Unity by fulness; All beings obtained Unity by life; [Heir] and people obtained Unity by being under the rule of Heaven. These all obtained permanence by Unity.
The innermost of Heaven is purity, if not so, it would be obscured; The innermost of Earth is repose, it not so, it would disintegrate; The innermost of spiritual beings is lack of bodily form, if not so, they would die; The innermost of valleys is fulness of water, if not so, they would be sterile; The innermost of creatures is life, if not so, they would perish. The high honour of [heir] and people is in their being together under the rule of Inner Life, if not so, they would soon lose harmony, The root of honour is in humility, The standpoint of high estate is in lowliness. That is why [heirs] and [kings] call themselves orphans, solitary [people], chariots without wheels.
The active principle of their Unity is in lowliness. Who can deny this? If you take a chariot to pieces, you have no chariot (it has lost its Unity). Do not desire to be isolated as a single gem, nor to be lost in a crowd as pebbles on the beach.
The Long of iT:
Lao Tsu mentions unity in other chapters as well (10 and 22), but focuses intently on it in Chapter 39.
All elements of our Universe come into being because of unique, paradoxical circumstances (unity). Unity is the tension between linked elements that cannot escape each other. If linked things don’t repel each other in some way, they will fall apart. Or nothing will occur in the first place. That’s the paradox of life. It will not maintain (or occur) without a good reason, without a push. Tension is the push. Tension is the paradox. And life must have paradox to exist.
-TB