Why does it say "Evtach v'Lo Efchad"?
Malbim: I trust that I will not return to exile; the salvation is permanent. There are two reasons for this. (a) One who trusts in man fears lest the savior die or weaken. Kel is Yeshu'asi! Therefore, "Evtach" (in the present). (b) One who is helped fears lest the help will not be constant, but not one who is saved. The former is primary, and the help is secondary. One who is saved does not do anything; the savior does everything. If Hashem's salvation is via people's deeds, this is called help. Then, if their deeds worsen afterwards, He will hide His face. If the salvation is due to Chesed, not based on deeds, there is no fear for the future - "v'Lo Efchad."
What is the meaning of "Azi v'Zimras Kah Hashem va'Yhi Li li'Yshu'ah"?
Rashi: The strength and praise of Hashem was for me a salvation 1 . "Va'Yhi Li li'Yshu'ah" is like Hayah 2 Li li'Yshu'ah. Verses speak like this - "va'Asher Lo Sam Libo
Rashi: Do not say that Azi is my strength. We never find Azi with Chataf Kamatz [under the Ayin], rather, Shuruk, except for three places where it is Samuch to v'Zimras.
I.e. it is proper to express the past via the prefix Vov and future tense only when telling what happened in sequential order (PF); refer to Bereishis 4:1:1:1*.
Rashi: It is not like v'Zimrasi, rather, it is Samuch to the next word. Therefore, I say that the Yud in Azi is [extra,] like the Yud in "Shochni Sela" (Devarim 33:16).
Ibn Ezra (Shemos 15:2): Hashem is my might and the song of my praise; it is as if it says Azi v'Zimras Uzi.
Why does it say "Kah Hashem"?
Rashi: Until now, His name was divided. With the fall of Amalek, it became complete. Similarly, "Ki Yad Al Kes Kah" (Shemos 17:16, based on Midrashim): Hashem's throne and name are not complete until Hashem will make war with Amalek.
