This is another oracle against Moab and another (false?) lament for Moab who will be brought into ruin. Moab is personified as a person who at one time was strong, but now has been brought low along with all of his followers and all of his agricultural yields. The complete destruction of Moab is described in these verses.
If you look at the middle of vs.4 through 5 you see the end goal of the writer. He tells us that “when the oppressor (Moab) is no more and the destruction has ceased, then a throne shall be established in steadfast love in the tent of David, and on it shall sit in faithfulness a ruler who seeks justice and is swift to do what is right.” He gives a very different juxtaposition between the ruler of Moab, who will be destroyed primarily because he is unjust and not like the ruler who is described, and David. There can be no greater difference.
David is describe as a ruler that the Lord would want. Someone who is established in steadfast love. This is not normally a description that we might seek after for our ruler. David as King is described as faithful and whose primary desire is for the good of the nation. That is an assumption that we make when we think of our ruler, that their primary goal is the good of the nation. The ruler is someone who is described as seeking justice. That is definitely an attribute that we would want in our ruler, someone who understood what justice was and would pursue it. Finally, the ruler is described as someone who is swiftly able to do what is right. A ruler whose moral compass is not wavering. A ruler who has all of these attributes is possible, but we sometimes settle for something far less than what is described in these verses.