Jeremiah 1:2

In the thirteenth year of his reign. — If we take the data of 2 Kings 22, Josiah was at that time in his twentieth or twenty-first year, having grown up under the training of Hilkiah. His active work of reformation began five years later. The images of Baal and Asherah (the groves) were thrown down, and the high places desecrated. The near coincidence of the commencement of Jeremiah’s work as prophet with that of the king must not be forgotten. As Josiah reigned for thirty-one years, we have to place eighteen years of the prophet’s ministry as under his rule.