1)
What do we learn from "Ki Ein Lavo El Sha'ar ha'Melech bi'Lvush Sak"?
1.
Torah Temimah citing Brachos 62b: Sackcloth is not repulsive, yet it is improper in front of a mortal [king]. Spitting is disgraceful. All the more so it is forbidden in Har ha'Bayis, in front of the King of kings!
2.
Rashi: It is improper to come to Sha'ar ha'Melech wearing sackcloth.
3.
Vilna Gaon: He wanted to come, but he could not, due to his sackcloth.
4.
Malbim: He came in front of Sha'ar ha'Melech, so the matter will be known in Sha'ar ha'Melech, to Esther or to the king himself. It is not normal to go in front of Sha'ar ha'Melech in sackcloth, so this will be publicized in Sha'ar ha'Melech.