Why does the Torah refer to the fire on the Mizbe'ach as "Eish Tamid"?
Rashi: To indicate that the fire that is used to kindle the Menorah (which is called "Ner Tamid") 1 is taken from the Mizbe'ach ha'Olah.
Why does the Torah repeat "Lo Sichbeh" (See Pasuk 5)?
Rashi 1 : To teach us that whoever extinguishes the fire on the Mizbe'ach transgresses two La'avin.
See also Ibn Ezra.
What does "v'Hishbati Chayah Ra'ah min ha'Aretz"?
Ramban (citing R. Yehudah in the Toras Kohanim): It means that Hashem will remove them completely. 1
Ramban #2 (citing R. Shimon in the Toras Kohanim) and Targum Yonasan: It means that Hashem will withdraw from them the mandate to harm people. 2
Ramban: Because, since life is throbbing and the towns are full of people, the wild beasts will avoid them.
On Shabbos we offer only two Temidim and two Musafim. The fire will extinguish quickly! The verse did not mention fire from Heaven!
Moshav Zekenim (5): Just like the Ner Ma'aravi burned the entire day until the time of Shimon ha'Tzadik, miraculously, so the Ma'arachah burned the entire day. 1
Moshav Zekenim (5, citing R. Yehudah ha'Chasid): "Lo Seva'aru Esh b'Chol Moshvoseichem", but you may kindle on the Mizbe'ach and in Beis ha'Mokad even on Shabbos.
Why do we say that the Menorah is testimony to the world that the Shechinah dwells amidst Yisrael.(Shabbos 22b)? Only Kohanim may enter the Heichal and see it. Yisraelim may enter the Azarah and see the Mizbe'ach! The Menorah was every day, but the Mizbe'ach was only on Shabbos. Also, people might think that there are kinds of wood (perhaps after special treatment) that burn an entire day, but surely, based on nature, the Ner Ma'aravi should not burn longer than the others. (PF)