Why does it say "va'Yisyatzev"?
Radak: This time, Shmuel saw a prophetic vision in front of his eyes. This is like "va'Yisyatzev Mal'ach Hashem ba'Derech Eretz" (Bamidbar 22:22).
Malbim: Really, this expression applies only to physical beings. It is 'borrowed' to refer to a prophetic image. Hisyatzvus implies that is need to be strengthened to persist there. A physical body must be strengthened to cling to something spiritual.
Why did He say "Shmuel" twice, and similarly regarding Avraham, Yakov and Moshe (Bereishis 22:11, 46:2, Shemos 3:4)?
Tosefta (Brachos 1:14): It shows endearment, and making zealous. They were the same before Hashem spoke to them, and before they were aggrandized, and after.
Malbim: This is to arouse both parts - the spiritual and physical - to be ready to hear Hashem's words.
Eli told him to say 'Daber Hashem'. Why did Shmuel omit Hashem's name?
Rashi (from Shabbos 113b): Shmuel thought, perhaps it is another voice (Radak - i.e. a Shed. 1 This Drashah is difficult.)
Radak: He was afraid to mention Hashem's name in a prophetic vision.
The Gemara said only that he was a Chacham to omit Hashem's name. Rashi there explained, lest it is not the Shechinah. The Ra'avad on Tamid (printed on Daf 34a) says that there is no concern for demons in the Mikdash! Yabi'a Omer (4 OC 1, citing the Sho'el u'Meshiv's Haskamah to Yehudah Ya'aleh) says that perhaps there was concern in Mishkan Shilo, whose Kedushah was not permanent.
