former things
That is, Isaiah's prediction of Sennacherib's invasion and its results, Isaiah 10 and 37. See also, (Isaiah 41:21-23); (Isaiah 43:8-12); (Isaiah 44:7); (Isaiah 48:3); (Isaiah 48:5); (Isaiah 48:16). This appeal of the prophet to the fulfilment of his former predictions strongly confirms the unity of the book.