spontaneously.[3]
Heaven and Earth unite to drip sweet dew, Without the command of men, it drips evenly over all.[4]
Once a system comes into being, Names are instituted.[5]
Once names are instituted, One has to know where and when to stop.
It is by knowing where and when to stop That one can be free from danger. Everything under Heaven is embraced by the Dao, Just like every river or stream running into the sea.[6]

Annotations:
[1] This proposition is, with regard to the eternity and unnameability as basic features of the Dao, first put forth by Lao Zi in Chapter 1 (see Part I, 1.1) and then repeated in other chapters, such as 37 and 41 apart from this one.
[2] The Chinese word pu means "simple" or "simplicity," which is characteristic of the Dao, according to Lao Zi. The word xiao literally means "minute" but actually implies the ability of the Dao to permeate everything. Lao Zi describes the Dao as both da (great) and xiao (minute):
The former refers to the all-embracing and omnipotence of the Dao (see chapters 25, 14, in Part I, 1.4 and 2.1), and the latter to the all-permeating capacity of the Dao as presented in this context. A relevant interpretation is found in Zhuang Zi's remark that "the Dao is great without an outside and minute without an inside."
[3] This exemplifies the appealing gravity of the Dao that makes people willing to be the subjects of the kings and lords who have applied the Dao to their government.
[4] The Chinese expression gan lu sometimes means "sweet dew" and sometimes "rainfall." It falls upon all things alike without preference precisely because of the action of the Dao.
[5] Historically speaking, once zhi (social system) was formulated and established, the naming and ranking of the people and things were launched. This resulted in a variety of names, titles, roles and positions.
[6] The Dao is figuratively likened to "the sea" because of its vastness and boundlessness, which can accommodate "every river or stream." In other words, the Dao itself can be boundless enough to accommodate all under Heaven.

Commentary:
Lao Zi makes simplicity a characteristic of the Dao, which in turn reflects the primitiveness of the Dao. This notion in fact signifies the way of spontaneity (i.e. naturalness) and take-no-action. If a leader can hold on to it and put it into social practice, they are sure to win the people over and govern the country in peace.
Da (great) and xiao (minute) are obviously antithetic in common sense, but implicitly interrelated in the functioning of the Dao, somewhat similar to you (being-within-form) and wu (being-without-form) as two complementary aspects of the Dao. Both da and xiao are abstract terms. The former suggests that the Dao embraces and covers all to the extent that "when meeting it, you cannot see its head; while following it, you cannot see its back." This implies that the Dao is invisible and formless to the extent that it permeates and determines everything everywhere.
The "sweet dew" as a product of the Dao "drips evenly over all." This demonstrates that the Dao treats all things alike, as though it embodies a spirit of equality. Modest and accommodating, the Dao receives all things in the way the sea conceives every river and stream. Hence it becomes boundless and inexhaustible. Even so, it does not claim any glory for itself but lets things be what they are. The parabolic depiction of the Dao through the image of the sea also carries the message that the Dao renews itself due to its receptiveness. It is something that remains open to all for ever. This is compatibly true of Lao Zi's philosophical system that always produces new and instructive findings whenever it is read and reread.
As mentioned in this chapter, Lao Zi reminds people of the importance of knowing where and when to stop once names were assigned. This in fact advises people to bridle their desires and to be contented with what they have. Otherwise they may get into trouble in the course of their hot and blind pursuit of external temptations.
4.3 (Chapter 34)
The great Dao flows everywhere.[1]
It may go left, it may go right.

(1)(2)(3)(4)