The chapter opens with an observation about drainage and turns it into a rule for holding office. The reason rivers and seas are able to be kings of the hundred valleys is that they are good at lying below them.
The word kings is not decoration. In the geography the image assumes, every stream in a range runs down to the same river, and the river receives all of them without summoning any. That is a real relation of dominance produced entirely by position, and the chapter treats it as a model of authority rather than as a metaphor for humility.
The rule drawn from it is stated twice, once for speech and once for position. One who wants to be above the people must in speech put himself below them. One who wants to be in front of the people must put himself behind them.
The two clauses are not the same instruction. The first concerns how a ruler talks, which connects to chapter thirty-nine and the titles by which rulers call themselves orphaned and unworthy. The second concerns where he stands in an order of precedence, and it is the harder of the two.
The results are stated in terms of what the people do not feel: he is above and they are not weighed down, in front and they are not harmed. That is a distinctive measure of good government. The chapter does not claim the people are grateful or prosperous, only that the weight of being governed is not registering, which is the same standard chapter seventeen sets when the best ruler is barely known to exist.