You are to go: You is emphatic in Hebrew. The sense is “you must go instead [of me]” (Contemporary English Version).

A fast day: There were certain days appointed for fasting, but fasts were also held at times of approaching national disaster. On such occasions large numbers of people would gather in the temple. Translators must avoid giving the readers the impression that the people were not eating because there was no food. A fast day can be “a time when the people do not eat in order to call for God’s help” or “a time when the people don’t eat so as to gain the LORD’s favor.”

Scroll is not the full form, as in verses 2 and 4, but the usual abbreviated form of the word.

In the hearing of all the people … in the hearing of all the men of Judah who come out of their cities: The text could make it seem that after reading to the people Baruch was to do a separate reading for the men of Judah (which here means “the people of Judah”), but in fact, as is clear in Good News Translation, the meaning is that he should read so all the people, including those from the towns of Judah, can hear. Who come out of their cities refers to people who have come to Jerusalem for the day of fasting from their own towns and villages away from the big city; see Good News Translation “who have come in from their towns.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on Jeremiah. (UBS Helps for Translators). New York: UBS, 2003. For this and other handbooks for translators see here .