18 The instruction to “open your mouth” is a metonymy of cause; it means “speak up for” (so , , ) or in this context “serve as an advocate in judgment” (cf. “you must defend”).
19 The instruction compares people who cannot defend themselves in court with those who are physically unable to speak (this is a figure of speech known as hypocatastasis, an implied comparison). The former can physically speak; but because they are the poor, the uneducated, the oppressed, they are unable to conduct a legal defense. They may as well be speechless.
20 Or “of all the defenseless.” The noun חֲלוֹף (khalof) means “passing away; vanishing” (properly an infinitive); in this construction “the sons of the passing away” means people who by nature are transitory, people who are dying—mortals. But in this context it would indicate people who are “defenseless” as opposed to those who are healthy and powerful.
21 The noun צֶדֶק (tsedeq) serves here as an adverbial accusative of manner. The decisions reached (שְׁפָט, shéfat) in this advocacy must conform to the standard of the law. So it is a little stronger than “judging fairly” (cf. , ), although it will be fair if it is done righteously for all.
22 Previously the noun דִּין (din, judgment”) was used, signifying the legal rights or the pleas of the people. Now the imperative דִּין is used. It could be translated “judge,” but in this context “judge the poor” could be misunderstood to mean “condemn.” Here advocacy is in view, and so “plead the cause” is a better translation (cf. , , “defend the rights”). It was—and is—the responsibility of the king (ruler) to champion the rights of the poor and needy, who otherwise would be ignored and oppressed. They are the ones left destitute by the cruelties and inequalities of life (e.g., 2 Sam 14:4–11; 1 Kgs 3:16–28; Pss 45:3–5, 72:4; Isa 9:6–7).