The second introductory formula Thus says the LORD of hosts often follows the previous formula at the beginning of longer paragraphs (compare Hag 1.2; Hag 2.11; Zech 8.2, 19) and may be seen as a marker of subdivisions within the paragraph (see the comments on 8.1-17). For LORD of hosts, see the comments on Hag 1.2.
The words that follow are in fact a repetition of the ethical teaching typical of the eighth century prophets. Good News Translation makes it clear that these are not original ideas of Zechariah by translating Thus says the LORD of hosts as “Long ago I gave these commands to my people.” Contemporary English Version has “So once again, I, the LORD All-Powerful, tell you.” (The change to first person “I/my” is part of the stylistic restructuring that Good News Translation and Contemporary English Version carry through the whole paragraph. See the introductory comments on this section.)
Render true judgments, show kindness and mercy each to his brother: These are general statements of the principles underlying sound social and personal relationships. Good News Translation expresses the first in modern language as “You must see that justice is done.” Translators could also say, “Apply the law fairly” (Jerusalem Bible/New Jerusalem Bible). The context here is a legal one. For this command compare Isa 1.17; Jer 21.12; Jer 22.3; Amos 5.14-15, 24.
For an emphasis on the quality of kindness, compare Hos 4.1 and Micah 6.8. The Hebrew word chesed here translated kindness was particularly associated with loyalty to the obligations accepted when a person entered into a covenant relationship. It was thus expected that the Jews, as a people having a covenant relationship with God, would show this quality in their attitudes both to God and to one another. Mercy is translated “compassion” in Moffatt, New American Bible, Jerusalem Bible/New Jerusalem Bible, New English Bible/ Revised English Bible, and New International Version. Each to his brother is the Hebrew way of saying “to one another” (Good News Translation, Contemporary English Version). Brother does not mean only close relatives, or only male relatives, and this should be made clear.
Quoted with permission from Clark, David J. & Hatton, Howard A. A Handbook on Zechariah. (UBS Helps for Translators). New York: UBS, 2002. For this and other handbooks for translators see here .