1)
What is the significance that he was on the wall?
1.
Malbim: This weakens the soldiers, for they see that the king despaired.
2)
What is the meaning of "ha'Sak Al Besaro mi'Bayis"?
1.
Rashi: (He had sackcloth on his skin, under his royal garments.) Through the tear [in his royal garments], they could see the sackcloth underneath.