2 in the first year of his reign, I, Daniel, perceived in the books the number of years which, according to the word of the Lord to Jeremiah the prophet, must pass before the end of the desolations of Jerusalem, namely, seventy years. 3 Then I turned my face to the Lord God, seeking him 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.