What are the implications of the words "v'Hechezakta Bo"?
Rashi: It means that one should support him, to prevent him from falling any further. 1
Moshav Zekenim: The Hei is extra, to teach that one must support him even four or five times.
Rashi: This can be compared to a load on a donkey; as long as it is still on the donkey's back, one person can grab hold of it and support it. However once it has fallen to the ground, even five people cannot prop it up.
Who is "Achicha" that one is obligated to support?
Ibn Ezra: It is a Jew.
Moshav Zekenim: "Imach" excludes one who departed from the way of Torah. One might have thought that even though he sinned, he is called "Achicha". Really, he is still called Yisrael, but not Achicha. 1
What is the meaning of "Ger v'Soshav"?
Rashi (based on Toras Kohanim): "Ger" refers to a Ger Tzedek; "Toshav", to a Nochri who has undertaken not to worship idols (and to observe the other six Mitzvos B'nei No'ach, and whom one is obligated to sustain - Rashi in Avodah Zarah, 20a), even though he eats Neveilos.
Targum Onkelos (according to Ramban, Ba'al ha'Turim ha'Aruch 1 ): These are verbs; the entire verse discusses Achicha
Their text of Onkelos was 'Yidor v'Yitosav.' According to this, there is no Mitzvah to support a Ger Toshav! This Perush resolves four difficulties of Rashi's (the accepted) Perush (refer to 25:35:3:1). (a) Why is "va'Chai" singular? (b) According to Rashi, the Asnachta should be on "Bo", for until "Bo" discusses Achicha. (c) Why is a Ger Toshav mentioned here? One may take Ribis from him! (d) Tosfos (Bava Metzi'a 111b DH mi'Gercha) asked that a convert is already included in "Achicha"! (Also see question 25:35:151
What are the ramifications of the phrase "va'Chai Imach"?
Ramban #1: Based on the implication from the word "Imach" - that your life takes precedence over that of your fellow-Jew - it teaches us the Mitzvah of self-preservation. 1
Ramban #2 (citing Targum Onkelos) and Targum Yonasan: It is a Mitzvah to sustain the stranger and the Toshav.
Ramban (citing the Toras Kohanim): As R. Akiva countered ben Putiri (who, in the case of Reuven and Shimon who were traveling in the desert, based on the Pasuk "va'Chei Achicha Imach", and Reuven had sufficient water for one person, ruled that they should share it) and, based on the same Pasuk, ruled that Reuven's own life takes precedence over Shimon's. The Ramban is referring basically to this Pasuk (and "ve'Chai Achicha Imach" is a repetition that comes to emphasize the issue (See R. Chavel's footnotes).
Rashi writes that one must support even a Ger Toshav. If so, all the more so a Jew and convert. Why did the Torah need to write Achicha and Ger?