Sitting on the ground symbolized sadness and distress. So this is another image from Isaiah that expresses the fate of the nation of Judah if she continued on her present course (read Isaiah 3:24).
When Job’s friends came to comfort him, they did not say a word for seven days, but “they sat down with him upon the ground. . .for they saw that his grief was very great” (Job 2:13). The same idea of despair is also expressed in these declarations: “Wallow thyself in ashes” (Jeremiah 6:26) and “roll thyself in the dust” (Micah 1:10).
ISAIAH 3:26 – Her [Jerusalem’s] gates shall lament and mourn; and she being desolate [destitute, NIV] shall sit upon the ground.