Keil & Delitzsch

The prophet now exclaims to the afflicted church, in language of unmixed consolation, that Jehovah is coming. "Strengthen ye the weak hands, and make the trembling knees strong! Say to those of a terrified heart, Be strong! Fear ye not! Behold, your God will come for vengeance, for a divine retribution: He will come, and bring you salvation." Those who have become weak in faith, hopeless and despairing, are to cheer up; and the stronger are to tell such of their brethren as are perplexed and timid, to be comforted now: for Jehovah is coming nâqâm (i.e., as vengeance), and gemūl 'Elōhı̄m (i.e., as retribution, such as God the highly exalted and Almighty Judge inflicts; the expression is similar to that in Isa 30:27; Isa 13:9, cf., Isa 40:10, but a bolder one; the words in apposition stand as abbreviations of final clauses). The infliction of punishment is the immediate object of His coming, but the ultimate object is the salvation of His people (וישעכם a contracted future form, which is generally confined to the aorist).