Who says "Lechu v'Na'aleh"?
Radak: Every nation says to its fellow nation "Ki mi'Tziyon
Why is it called "Beis Elokei Yakov"?
Rashi (from Pesachim 88a): He called it Beis Kel, therefore it is called on his name. Avraham called it "b'Har Hashem Yera'eh" (Bereishis 22:15), and Yitzchak called it a field - "Lasu'ach ba'Sadeh" (Bereishis 24:63).
What is the meaning of "va'Yorenu mi'Derachav"?
Radak: Melech ha'Mashi'ach will teach us; it says about him "v'Shafat" (4).
Malbim: Derachim are the big roads; Archos are the small paths that branch off from them. Even though he will teach to us only the big paths 1 , which are the roots of the creed and its basis, we ourselves "Nelchah b'Archosav" the small individual paths. I.e. we will strive to understand the details and branches of the creed.
Malbim: Also, he will teach to us only mi'Derachav (some of the big paths); via diligence, we will grasp all of [even the small] the paths.
Why will Torah come from Tziyon?
Malbim: It was the place of the [great] Sanhedrin, Kohen Gadol and Malchus Beis David.
To where will Torah go out?
Malbim: To the entire world - ""Ki Yipalei Mimecha Davar la'Mishpat... v'Kamta v'Alisa" (Devarim 17:8), i.e. to Tziyon.
What is "Devar Hashem"?
