Behold, the former things are come to pass; i.e. former prophecies have been fulfilled. Israel has been led lute captivity, and in her captivity has suffered grievous things. The reference is, perhaps, especially to such prophecies as Isaiah 39:5-7.
And new things do I declare (comp. Isaiah 43:19). The voluntary restoration of a captive people to their own land by the power to which they were subject, and which could compel their services, was emphatically a "new thing" in the world's history.
How unwilling the sovereign power was ordinarily to lose such services may be seen by the narrative in Exodus (Exodus 5-14.), and again by the account which Herodotus gives (1:73, 74) of the ground of quarrel between Alyattes and Cyaxares.
Before they spring forth; or, shoot forth. The metaphor is one taken from the vegetable world (comp. Isaiah 43:19; Isaiah 45:8).