What are the connotations of "u'Fanisi aleichem"?
Rashi: It means that Hashem will turn from all His other activities in order to reward us. 1
Targum Yonasan: It means that Hashem will turn from rewarding the nations in order to reward us.
Rashi: This can be compared to a king whose hired workers - except for one - did not perform their tasks properly. When they came to receive their remuneration, the king turned to the faithful worker and said to him 'My son; all your co-workers who did little work, I will pay a small wage; but with you, I have to make a large reckoning!' And so it is here; Hashem will quickly pay of the nations of the world, but when it comes to Yisrael, He will turn aside from all His occupations, because He needs time to pay them for all their good deeds (Sifsei Chachamim).
What is the difference between "Vehifreisi Eschem" and "Vehirbeisi Eschem"?
Rashi: "Vehifreisi Eschem" refers to increased numbers; "Vehirbeisi Eschem", to walking erect. 1
Ramban and Moshav Zekenim: "Vehifreisi Eschem" means 'You will all bear children' (not a man or woman among you will be barren); "Vehirbeisi Eschem," 'You will bear many children' (that no children will die at childbirth), and you will live long, so that you will become a vast nation.
See Sifsei Chachamim.
Which covenant is the Torah referring to?
Rashi: It is referring to a new covenant that Hashem will set-up with Yisrael, 1 not like the one at Har Sinai, which they abrogated.
Seforno: It refers to the covenant that Hashem made with Avraham - 'to be for him a G-d and his children after him', 2 which He will establish with them on their own merit, 3 not solely on the merit of the Avos. 4
Rashi: See Yirmiyah, 31:30, 31.
Seforno: Bereishis 17:7.
Seforno: Since the Torah adds the word "Itchem".
Seforno: As the Navi indicates in Yechezkel, 36:26 and in Yeshayah, 54:10.
QUESTIONS ON RASHI
Rashi writes that "Vehirbeisi Eschem" means 'erect'. But the Gemara in Kidushin 31a and OC 2:6 forbids walking completely upright? Moreover, Nochrim too, walk upright?
Tzeidah la'Derech (also cited in Yalkut Yosef 2, 14): Here, the Pasuk is referring to importance - inasmuch as man is greater than animals, since, as opposed to animals, who face the ground, he stands upright with his head facing upwards (towards the world of intellect).
Maharam Shik: Walking erect is forbidden regarding mundane issues, but it is appropriate for Torah. 1
Sukas David: The Isur is due to the fact that it is based on haughtiness - he feels that he has no master. Whereas here, Hashem is leading us this way, so the Isur does not apply.
The Gemara is referring to walking in a haughty manner - head held high, whereas Rashi means that Hashem will remove the yoke of the nations from us and we will be free to walk without fear. 2
Maharam Shik: As the Pasuk in Divrei ha'Yamim 2 17:6 indicates "Vayigba Libo be'Darchei Hashem".