2. understood by books—rather, "letters," that is, Jeremiah's letter (Jer 29:10) to the captives in Babylon; also Jer 25:11, 12; compare 2Ch 36:21; Jer 30:18; 31:38. God's promises are the ground on which we should, like Daniel, rest sure hope; not so as to make our prayers needless, but rather to encourage them.