What is the significance of the fact that Moshe warned Yisrael "Hishamru lachem ... ", whereas Bil'am spoke only of their praise - insinuating that everything was fine and nothing would happen to them ('Asu Ta'avaschem ve'Eino Makpid')?
Rashi (in Mishlei, Ibid.): Moshe (based on love) was rebuking them whereas Bil'am, who hated Yisrael, was flattering them - and the Pasuk writes in Mishlei 28:23 'One who rebukes a person will ultimately find favor more that one who flatters him'.
Why does the Torah issue the warning "Hishamru lachem ... " specifically here?
Rashi: Because it is when a person is satiated that he tends to lash out and rebel against Hakadosh-Baruch-Hu, as the Torah wrote in Eikev. 1
What is "Vesartem" referring to? What is the connection to the continuation of the Pasuk?
Rashi: It refers to the way of Torah and Mitzvos, and the Torah is teaching us here that, once one strays from the path of Torah and Mitzvos, one is bound to worship other gods and cleave to them. 1
Oznayim la'Torah: It is only after one strays from the path of Torah that one worships other gods. Otherwise, Hashem declares 'If only, when they forsook Me, they had still kept the Torah, the light in the Torah would have brought them back!' 2
Rashi: As David ha'Melech said in Shmuel 1, 26:19 "For they drove me away from cleaviing to the inheritance of Hashem (from Torah-study) saying 'Go and worship other gods!' - because once a person is exiled from studying Torah, he is but one step away from worshipping idols. Lev Eliyahu (Shemos p.92)
What are the implications of "Elohim Acherim"?
Refer to Shemos, 20:3:3:1 - 4 and notes.
What are the implications of "Pen Yifteh Levavchem"?
Lev Eliyahu (in Shemos, p.91): When a person's heart is blunted, lust takes over, one's intellect cannot stand against it, and one turns to idolatry.
