What is the calculation of 70 years in exile?
Radak: Refer to 25:12:1:1.
What is the significance of 70 years in exile?
Rashi (Vayikra 26:35): "The land will rest what it did not rest when you dwelled in it." They sinned 436 years, in which they did not observe 61 Shemitah years, eight Yovel years and a year that entered Shemitah 1 , 70 in all.
How did a year enter Shemitah? The Churban was in the year after Shemitah (Ta'anis 29a)! Sifsei Chachamim - a year is added, for Hashem exiled us [two years] early, lest we fulfill "v'Noshantem ba'Aretz" (Devarim 4:25). (This is difficult. The next two years were not Shemitah years! Why didn't Rashi say that there was a 62nd Shemitah year, or a ninth Yovel year? The years that they sinned were not consecutive! - PF)
What is the meaning of "Efkod"?
Radak, Malbim: I will arouse the spirit of Koresh Melech Paras, like it is written (Ezra 1:1). This Pekidah was 70 years from Malchus Bavel (Malbim - for then Malchus Bavel ceased). Binyan ha'Bayis was 70 years after Churban Yerushalayim, when Tzidkiyah was exiled (Malbim - 19 years after the Pekidah).
Why does it say "v'Hakimosi Aleichem Es Devari ha'Tov"?
Malbim: Hashem put a time limit on the exile, unlike Galus Edom, for which no limit was set; if we merit, Hashem will end it earlier. You are forced to say that Hashem saw with his Chachmah that they need to be in exile for this time 1 , for their benefit.
