Why did Hashem add the (otherwise superfluous) phrase, "Asher Mitzrayim Ma'avidim Osam" here?
Rashi: Because the covenant that He made with the Avos included punishing the Egyptians for enslaving their children. 1
See Bereishis 15:14.
QUESTIONS ON RASHI
Rashi writes: "'V'Gam Ani [Shama'ti...]' - Just as I established the covenant, I must fulfill it; therefore, 'I have heard the cries etc.'" What is Rashi clarifying?
Gur Aryeh: The opening word "Gam" (also) does not introduce a new idea (as in, 'And in addition, I have heard...'). Rather, it continues the idea that was begun in the preceding Pesukim (6:3-4) - 'Because I promised the Avos, and made a covenant, I must fulfill it (by accepting the Bnei Yisrael's cries, and redeeming them).'
Rashi writes: "... 'I have heard the cries of Bnei Yisrael' who are screaming, ... 'that Mitzrayim is enslaving them." What is Rashi adding with this phrase?
Gur Aryeh: The explanatory phrase, "that Mitzrayim is enslaving them," does not come to explain to which Bnei Yisrael the verse refers - there is only one! Rather, it explains why, and to what degree, they are crying out - it is due to their enslavement.
Rashi writes: "... 'And I remembered' [My covenant]' - ... At the Bris Bein ha'Besarim, I told [Avraham], 'Also the nation that they will serve, I shall punish!' (Bereishis 15:14)." Why does Rashi highlight that particular covenant here?
Gur Aryeh: Although the preceding verse (6:4) mentions only the covenant to give them the Land, - that was not why the Bnei Yisrael were crying out now! They were crying due to the harsh slavery [and it was at the Bris Bein ha'Besarim that Hashem promised to take them out of slavery, and punish their oppressors]. 1
Gur Aryeh: The sequence of Pesukim 6:3-6:8 should be explained as follows. 'I appeared to Avraham... and made a covenant to give his descendants the Land... I heard their outcry due to the slavery. I promised at the Bris Bein ha'Besarim to punish the Mitzrim, and I remember that I also promised to bring them to the Land. Therefore, say to Bnei Yisrael, 'I shall take you out... and I shall bring you to the Land....' Also see Mizrachi, and Gur Aryeh's response.