What is "Ehyeh Imach"?
Vilna Gaon: You will not be killed.
Why did He say "I cut off all your enemies from in front of you"?
Rashi: This is why you thought to build the Beis ha'Mikdash, based on Devarim 12:10-11.
Vilna Gaon: You will kill [them]. Malbim - In Shmuel II, 7:9 it says "va'Achrisah". The suffix Hei implies that it is not past tense, rather, it reveals desire.
Malbim (Shmuel II, 7:9): You do not have the absolute serenity required to build the Beis ha'Mikdash. Your enemies are cut off in front of you - but not in front of Yisrael, and they were not eradicated.
What is "k'Shem ha'Gedolim"?
'Rashi', Radak: It is like the great kings - "v'Yatza Shem David b'Chol ha'Aratzos va'Shem Nasan Es Pachdo Al Kol ha'Goyim" (14:17).
Vilna Gaon, Rashi (Shmuel II, 7:9 citing Pesachim 117b): Yisrael will say [at the end of the third Berachah after reading the Haftorah] 'Magen David' (similar to 'Magen Avraham'). Vilna Gaon - and fear of Hashem will be on all his enemies.
Malbim (Shmuel II, 7:9): Your kingship will be permanent, just like the name of the Gedolim endures.
