What is the meaning of "Hinach Harah"?
Radak: You will become pregnant.
Malbim: It is as if you are already pregnant; you must begin guarding [my commands] immediately.
Malbim citing Bamidbar Rabah 10:5: The semen was already in her womb, and conception occurred the moment he spoke to her. This is why above (verse 3) he said v'Haris (future), and now Harah (you are pregnant at this moment).
What conjugation is "v'Yoladt"?
Radak #1: It is a composition of Yoledes (present) and v'Yaladt (past with the prefix Vov, to convert it to future. 1 Because he said Harah, which is an adjective like Po'eles (present tense conjugation), he said also [Yoledes,] an expression of Po'eles regarding the birth. Since it will be in the future, he said [also] v'Pa'alt (future conjugation).
Radak #2: It is a verb form like Merubah. 2
What is the meaning of "u'Morah"?
Targum Yonasan: It is a razor. Rashi - it is called Morah, for it is Moreh 1 and casts [cuts] off hair.
Metzudas Tziyon: This is like "Yarah va'Yam" (Shemos 15:4).
Why does it say Yachel (he will begin) to save Yisrael from Pelishtim?
Mahari Kara: Since he will begin Nezirus in the womb, this will enable him to save Yisrael from Pelishtim.
Radak #1: The Shoftim before him did not fight the Pelishtim. 1
Radak citing Sotah 9b: Yachel hints that Huchlah (was profaned) Avimelech's Shevu'ah "Im Tishkor Li ul'Nini ul'Nechdi" (Bereishis 21:23). They fought first with Yisrael (so Yisrael were allowed to fight them).
Radak #2: It says he began, for it was not a total salvation.
Mahari Kara: This is wrong. Shamgar killed Pelishtim with a plowshare (3:11); Pelishtim and Amonim afflicted Yisrael (10:7, 8), and Yiftach saved them!
