Daniel 9:1,2

In the first year of Darius That is, immediately after the overthrow of the kingdom of Babylon, which was the year of the Jews' deliverance from captivity. This Darius was not Darius the Persian, under whom the temple was built, as some have asserted, to invalidate the credibility of this book; but Darius the Mede, who lived in the time of Daniel, and is called Cyaxares, the son of Astyages, by the heathen historians: see note on chap. Daniel 6:1. In the first year of his reign, I Daniel understood by books, &c. Namely, by the several prophecies of Jeremiah 25:11; Jeremiah 29:10, which are called so many books: see Jeremiah 25:13; Jeremiah 30:2. We may learn from hence, that the later prophets studied the writings of those prophets who were before them, especially for the more perfect understanding of the times when their prophecies were to be fulfilled. The same they did by several of their own prophecies. That he would accomplish seventy years, &c. Concerning the time from whence these seventy years are to be dated, see note on Jeremiah 25:11. Daniel saw a part of Jeremiah's prediction fulfilled, by the vengeance which the Lord had taken upon the house of Nebuchadnezzar; but he saw no appearance of that deliverance of the Jews which the prophet foretold. This was the cause of his uneasiness, and the motive of his prayers.