The most important teaching in this passage is contained in the sentence: ‘To know when to be satisfied and to restrain desire is to know the secret of longevity.’ This refers to the subtle point that in learning to have acceptance and overcoming negative emotions in the sense of your desires, you will be conserving your energy, feeding it back into yourself instead of wasting it.
A feeling of contentment and an understanding that you do not need to chase after more may be gained in a third-dimensional way, from a balanced name part, but a more complete understanding would come from the spirit. When you have that acceptance and control you will know the ‘secret’ – your third-dimensional efforts will lead you to it because they create finer energies which can be used by the Tao to complete the process.
You cannot force an understanding of Tao, it cannot be coerced. But the efforts you make create the possibility of the secret flowing through you. Your struggles are the little streams which accumulate to lead to the broad river of Tao.