understood = came to an understanding; perceived, or observed. Hebrew. bin, to separate or distinguish. Implying that he had not known this before.
by books = by the writings [of Jeremiah]. Jer_29:1, Jer_29:10, as well as Dan_25:11. Note the definite Article in the Hebrew.
the number of the years. Which were now drawing to an end.
the LORD. Hebrew. Jehovah.App-4.
Jeremiah. The passage was doubtless Dan_25:11-14; Dan_29:10-14.
accomplish = fulfil [within].
seventy years. Note the bearing of this on Dan_9:24.
the desolations of Jerusalem. From 479 to 409 B.C. See note on 2Ch_36:21. The "desolations" had therefore lasted 42 (6 x 7) years, and had yet 28 (4 x 7) years to run before they were "accomplished". We find the same subdivisions of the "servitude"; for from the first year of Nebuchadnezzar (496) to the decree of Artaxerxes (Astyages) (454) was forty-two years; and from the decree to the end of the servitude was twenty-eight years.