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Some comments from the NICOT-Jeremiah commentary (J. A. Thompson, p.490-91):
In both the OT and later rabbinic writings there are two facets of the doctrine of Messiah: teaching about the Messiah as a person, and teaching about the Messianic Age. We have these two aspects here with the person of the Messiah in v. 5 and the Messianic Age in v. 6 (cf. Isa. 11:1-5 and 6-16). In his days Judah will be "rescued," "delivered," "liberated," all possible translations of the verb tiwwasa'. [Niphal 3rd fem. sing. of yasa', "to save"; NWT has "saved" - Bobcat] . . . Jeremiah looked forward to a day when Judah would be released from all restraints. No longer would external foes or internal tensions trouble her. She would be "kept safe" (NEB), "saved" (RSV), would "triumph" (J. Bright). But in that day the whole family of Israel would share in the rule of the ideal king. Israel here refers to the northern kingdom. She too would live in safety. The theme of coming salvation for all Israel occurs in chapters 30 and 31.
As in Isa. 9:6 a symbolic name is given to the coming king, Yahweh sidqenu, Yahweh is our Righteousness. The interpretation of the name varies. It is probably a play on the name of Zedekiah, sidqi-yahu, My righteousness is Yahweh. The noun sedeq was firmly anchored in the concept of kingship in Israel, and it would not be surprising for a king to take such a name as Zedekiah. If the king failed to live according to the symbolism of his name, "Yahweh is my righteousness," it would be appropriate for a prophet to draw the contrast as though to say: "but our Righteousness is Yahweh." In general the term sedeq denotes "what is right," "according to the norm," and hence, what is just. In some cases where Yahweh, or a king, sets to establish the right, the word (or its feminine form s e daqa) comes to mean the justice done in favor of someone, or vindication (Isa. 41:2, 10; 58:8; 62:1, 2) The plural sedaqot means "saving acts" (Judg 5:11; 1 Sam 12:7; Isa 45:24; Mic 6:5; Ps 103:6) Hence the symbolic name could mean "Yahweh is the vindication of our right" or "Yahweh is our Justice." The term must be allowed to take on its full meaning, which includes the saving presence and activity of Yahweh. The name is different from Zedekiah's name in that the pronouns are different and the position of Yahweh is different. The name Zedekiah could mean "Yahweh is my vindication." A play on the name seems evident and the oracle can therefore be dated during the reign of that king [Zedekiah]. . .
Clearly the oracle was a solemn one and pointed to a new era. Probably Jeremiah had in mind an ideal ruler who was closely bound to history. The forthcoming age was not seen as something reserved for the eschatalogical era, but as coming at the end of a particular era that had been marked by a failure in the functioning of the kingship in the context of the covenant.
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