It (Tao) is eternally without desire. So, it can be called small. All things return to it, although it does not make itself their ruler. So, it can be called great.
Heaven and Earth last for ever. Why do Heaven and Earth last for ever? They are unborn, so ever living. The sage stays behind, thus he is ahead. He is detached, thus at one with all. Through selfless action, he attains fulfillment.