Jeremiah 29:12,13 - Ellicott's Commentary On The Whole Bible

Then shall ye call upon me... — The words need no comment, but they cannot be passed over without dwelling on the infinite tenderness which they manifest in the prophet’s soul, the reflex of a like tenderness in the mind of God, from whom he gives the message. It is the anticipation of the like message from the lips of Christ, “He that seeketh findeth, and to him that knocketh it shall be opened” (Matthew 7:8). As they stand, the words are an echo of Deuteronomy 4:29-30, as Jeremiah 29:14 is of Deuteronomy 30:3-5.