9. For--The blessed things promised in this and Zep 3:10 are the immediate results of the punishment inflicted on the nations, mentioned in Zep 3:8 (compare Zep 3:19).
      turn to the people a pure language--that is, changing their impure language I will give to them again a pure language (literally, "lip"). Compare for this Hebrew idiom, 1Sa 10:9, Margin. The confusion of languages was of the penalty sin, probably idolatry at Babel (Ge 11:1-6, Margin, where also "lip" expresses language, and perhaps also religion; Zep 3:4, "a tower whose top may reach unto heaven," or rather, points to heaven, namely, dedicated to the heavens idolized, or Bel); certainly, of rebellion against God's will. An earnest of the removal of this penalty was the gift of tongues on Pentecost (Ac 2:6-13). The full restoration of the earth's unity of language and of worship is yet future, and is connected with the restoration of the Jews, to be followed by the conversion of the world. Compare Isa 19:18; Zec 14:9; Ro 15:6, "with one mind and one mouth glorify God." The Gentiles' lips have been rendered impure through being the instruments of calling on idols and dishonoring God (compare Ps 16:4; Ho 2:17). Whether Hebrew shall be the one universal language or not, the God of the Hebrews shall be the one only object of worship. Until the Holy Ghost purify the lips, we cannot rightly call upon God (Isa 6:5-7).
      serve him with one consent--literally, "shoulder" or "back"; metaphor from a yoke, or burden, borne between two (Nu 13:23); helping one another with conjoint effort. If one of the two bearers of a burden, laid on both conjointly, give way, the burden must fall to the earth [CALVIN]. Christ's rule is called a burden (Mt 11:30; Ac 15:28; Re 2:24; compare 2Co 6:14 for the same image).

JFB.