Jeremiah said that 70 years of exile in Babylon (see Jeremiah 25:11–12; 29:10) would compensate for the Sabbath years of rest that the land missed for nearly 500 years (2 Chronicles 36:21; see Exodus 23:10–11; Leviticus 26:34–35).
The summer fast mourned the destruction of Solomon’s temple (Zechariah 7:3), while the early autumn fast either marked the assassination of Gedaliah, governor of Judah (see 2 Kings 25:22–25; Jeremiah 41:1–3), or it was the day of atonement (Leviticus 23:26–32).