2 in the first year of his reign, I, Daniel, have understood by books the number of the years, (in that a word of Jehovah hath been unto Jeremiah the prophet,) concerning the fulfilling of the wastes of Jerusalem—seventy years; 3 and I set my face unto the Lord God, to seek 'by' prayer and supplications, with fasting, and sackcloth, and ashes.
Matthew Henry's Commentary on Daniel 9:2-3
Commentary on Daniel 9:1-3
(Read Daniel 9:1-3)
Daniel learned from the books of the prophets, especially from Jeremiah, that the desolation of Jerusalem would continue seventy years, which were drawing to a close. God's promises are to encourage our prayers, not to make them needless; and when we see the performance of them approaching, we should more earnestly plead them with God.