1)
What is "Te'alah"?
1.
Rashi: It is a trench.
2)
Why did he make a trench?
1.
Malbim: It was in order to have a miracle with the water (that the fire would consume it).
3)
What was "k'Veis Sasayim"?
1.
Rashi: The width was Beis Sasayim (Radak - the area in which one seeds two Sa'im of seeds; Chachamim estimated that this is), 100 by 50 [Amos], like Chatzer ha'Mishkan. Malbim - this is the limit that Hashem set for how far Kedushah (Machaneh Shechinah) spreads around the Mizbe'ach.
