Isaiah 42:9

Behold, the former things are come to pass, and new things do I declare: before they spring forth I tell you of them.

Behold, the former things are come to pass - the former predictions of God, which were now fulfilled, are here adduced in proof that they ought to trust in Him alone as God; namely, the predictions as to Israel's restoration from Babylon.

And new things do I declare - namely, predictions as to Messiah, who is to bring all nations to the worship of Yahweh (; ; ).

Before they spring forth I tell you of them - the same image from plants springing forth, i:e., just beginning to germinate, occurs, ; . Before there is the slightest indications to enable a sagacious observer to infer the coming event, God foretells it.