One who is filled with the Tao
is like a newborn child.
The infant is protected from
the stinging insects, wild beasts, and birds of prey.
Its bones are soft, its muscles are weak,
but its grip is firm and strong.
It doesn't know about the union
of male and female,
yet his penis can stand erect,
because of the power of life within him.
It can cry all day and never become hoarse.
This is perfect harmony.

To understand harmony is to understand the Constant.
To know the Constant is to be called 'enlightened'.
To unnaturally try to extend life is not appropriate.
To try and alter the life-breath is unnatural.
The master understands that when something reaches its prime
it will soon begin to decline.
Changing the natural is against the way of the Tao.
Those who do it will come to an early end.