What does "v'Af Gam Zos" imply?
Rashi: It implies that, even though Hashem will carry out the aforementioned curses regarding them, He will not reject them completely, to annul the covenant that He entered into with them.
Why are the connotations of the multiple expressions "Lo Me'astim, v'Lo Ge'altim, Lechalosam, Lehafer Brisi Itam"?
Targum Yonasan: The four expressions refer to the four exiles - Bavel, Madai, Yavan and Edom, respectively. 1
Meshech Chachmah: Even if Yisrael become lowly amids their exile and wants to abandon their heritage and be like the Nochrim, and think that Berlin is Yerushalayim - Hashem will not allow this. He will keep a remnant to Zera Avraham to found their Divine mission in Eretz Yisrael.
To inform us that Hashem will see us through each Galus and deliver us from the clutches of our oppressors.