1)
Why did he mention their afflictions due to sin, and the salvations?
1.
Malbim: Even when you sinned, Hashem's Hashgachah did not leave you. (a) At the time of rebellion, He punished you like a father chastises his son. (b) When you returned to Him, He immediately saved you.
2)
Why does it say "va'Yimkor? and va'Yilachamu Bam"?
1.
Malbim: Sometimes the enemy totally ruled over them, e.g. Sisera and Pelishtim in the days of Shimshon, and sometimes they merely made war, e.g. Pelishtim in the days of Shmuel and Mo'av (with Amon) in the days of Yiftach.
