Why will they cry between the Ulam and Mizbe'ach?
Radak: That is where they stand to do their Avodah. When the Avodah ceased - "Hachras Minchah va'Nesech" (1:9), they will stand there, cry and pray to Hashem, and say "Chusah..."
Malbim: Initially, Kohanim gathered the nation. Here, it was not needed. It did not say what the Kohanim will do! Therefore, it says that they will cry and pray between the Ulam and Mizbe'ach.
What is the significance of "Chusah Hashem Al Amecha"?
Malbim: Have compassion on them because they are Your nation, and You are King over them. (b) The land is Your Nachalah (inheritance). 'Nachalah' hints to its Kedushah.
What is "l'Cherpah?
Rashi: It is blasphemy.
Radak: Refer to 2:17:3:2.
Malbim: The land is Your Nachalah (inheritance). 'Nachalah' hints to its Kedushah. Your Shechinah dwells on it, due to its Kedushah. Therefore, do not let it be disgraced - "Lamah Yomeru va'Amim Aye Elokeihem."
What is the meaning of "li'Mshal Bam Goyim"?
Rashi: It is an expression of "l'Mashal veli'Shninah" (Devarim 28:37 - people will talk about them, and say 'so happened to Ploni').
Radak: When there was hunger in Eretz Yisrael, many went to live in Egypt and Eretz Pelishtim. This was shame for them, and Goyim ruled over them when they were in the Goyim's land.