Where were the faces?
Malbim: The human face was in front. On the right was a lion, on the left was an ox, and in back a Nesher. Midas ha'Chesed uses the right, fear uses the left, and Tif'eres is in the middle, a mix of Din and Chesed. An Eshes Chayil is in the back of the house, in back of the Mishkan, like a Nesher hovering over its chicks; so Midas ha'Malchus receives and influences below. When light explodes on His angels in Olam ha'Yetzirah, the right is seen as a lion, to show that Chesed will overpower like a lion with great strength. The left appears like an ox, lest Midas ha'Din come out with a strong hand and burning venom. Just the contrary "v'Rav Tevu'os b'Cho'ach Shor" (Mishlei 14:4). In the middle is "Emes l'Yakov" (Michah 7:20) to mediate between them. Its face is human; its Midah is mercy. In back is Pnei Nesher; its nature is to fly high to receive [influence], and "k'Nesher Ya'ir Kino" (Devarim 32:11) to influence on its chicks.
What is the significance of these four species?
Radak (28, citing Mechilta Yisro 19:11): On the day of Matan Torah, Yisrael saw the Merkavah, like Yechezkel. The smallest woman of Yisrael was great like Yechezkel. They saw the face of an ox opposite their camp, therefore they made an Egel. These four faces were on the Degalim - Yehudah's Degel was Pnei Arye ("Gur Aryeh Yehudah"), Reuven's Degel had a human face ("va'Yimtza Duda'im ba'Sadeh" - they have a human form). Efrayim's Degel had Pnei Shor - ("Bechor Shoro Hadar Lo"). Dan's Degel had Pnei Nesher - "Yehi Dan Nachash Alei Derech" "Ef'eh v'Saraf Me'ofef 1 " (Bereishis 49:9, 30:14, Devarim 33:17, Bereishis 49:17, Yeshayah 30:6).
Malbim: Bavel received its strength from the lion. Bavel and Ashur, which were joint kingdoms, are compared to a lion - "Alah Arye mi'Subecho" (Yirmeyah 4:7). The first creature that Daniel saw was a lion. Hashem took this form to save His children - "Acharei Hashem Yelechu k'Aryeh Yish'ag" (Hoshe'a 11:10). Madai u'Faras were like Tif'eres Adam. They benefited Yisrael, and authorized them to build the Beis ha'Mikdash. Yavan received from the ox on the left, and said 'write for yourselves on the horn of an ox?' Even though their source was from harsh Midas ha'Din, they could not burn the Beis ha'Mikdash, for there is no venom in their source above. Romi is compared to a Nesher; it endured long, like a Nesher, which renews itself 10 times 2 . Daniel saw 10 horns in the fourth creature. Romi's flag has the form of a Nesher. Each of the four Chayos has all four faces, for the four kingdoms are always found in the world, just one overpowers over all, and it goes first and all go after it.
Radak explains Saraf Me'ofef to be a Nesher; it is mentioned with a snake, for also a Nesher has poison (Rashba Chulin 53a). (PF)
Rashi (Tehilim 103:5, citing a Midrash): There is a species of Nesher that when it gets old, it returns to youth. Radak (ibid. citing Rav Sadya Gaon) - it flies higher than all other birds, and approaches the heat of fire. It casts itself into water due to great heat, and returns to youth. It does so every 10 years. When it reaches 100, it does like always, and it dies in the sea.
Why does it not say 'u'Fnei Adam l'Arbatam', like it says about the other faces?
Malbim: We already know this from "Demus Adam la'Henah" (5).
Here it says that one of the faces was of an ox. Below (10:14), it includes the face of a Keruv, and there is no face of an ox!
Chagigah 13b: Yechezkel requested mercy - can a prosecutor (an ox, due to Chet ha'Egel) become an advocate?! Hashem changed it to a Keruv.
