Here Job replied to Eliphaz, a non-stop conversation of Job's friend to him. Miserable means painful advice. As Christian's, we have to listen to Godly advice and not into the worldly thing.
Job said, if you were in my place, I will encourage you. After fellowship you feel relieve. Gauntness narrowness.
Assails means to attack figuratively.
Jeer means to mock or boo.
The experience of Jesus Christ - was mocked.
Isaiah 50:6 I offered my back to those who beat me,
my cheeks to those who pulled out my beard;
I did not hide my face
from mocking and spitting.
Sack clothe picture of mourning. Life on earth is very short. You can find encouragement in the Lord, that's why you need to read God's word. And the Lord knows all your needs.