Where will you go out?
Rashi: From Galus.
To where will you return?
Radak: To your land.
Why does it mention returning in Shalom?
Malbim: This is unlike returning from Galus Bavel, when hatred was written against you. Also your leaving will be b'Simchah, unlike Yetzi'as Galus Bavel 1 amidst crying, under Madai u'Faras.
We find that they left Eretz Yisrael to go to Galus Bavel amidst crying. However, 'under Madai u'Faras' implies that Yetzi'as Galus Bavel refers to leaving Bavel's jurisdiction, when Bavel fell and Madai u'Faras took power. What is the source that they cried then? They were not forced to leave! Rashi (Ezra 3:12) says that they rejoiced that they left Galus! (Only elders cried at the start of Binyan Bayis Sheni, for they had seen Bayis Rishon. - PF)
Will the mountains and hills sing?
Rashi: They will give their Peros and vegetation to you, and their residents will benefit (some texts - sing).
Radak #1: This is a metaphor; the entire world will rejoice.
Radak #2: The mountains and hills are a metaphor for great people; trees of the field hint to lower people.
Malbim: This is a metaphor - if you will repent, all derivatives of nature will have Shalom with you.
What is the significance of clapping?
Radak: It is amidst Simchah, like "va'Yaku Chaf va'Yomeru Yechi ha'Melech" (Melachim II, 11:12). The Targum of "va'Yach" (Shemos 2:12) is u'Macha.
Malbim: This is to accompany the singing of the mountains and hills. This is a metaphor for the great Simchah. The previous sin will not block it.
