Adam Clarke on Isaiah 43:10

Ye (the Israelites) are my witnesses, and my servant (the prophet) whom I have chosen - That whatever has been said before concerning Sennacherib has been literally fulfilled. The prophet had predicted it; the Israelites saw it accomplished.

Before me there was no God formed, neither shall there be after me - This is a most difficult place. Was there a time when God was not? No! Yet he says, before me. Will there be a time in which God will not exist? No! Yet he says, after me. Are not all these words to be referred to his creation? Before me, no god created any thing, nor was there any thing pre-existent but myself. And after me, i.e., after my creation, such as now exists, there shall be no other class of beings formed. This mode of interpretation frees the passage from all embarrassment, and the context perfectly agrees with it. The words my servant, in this verse, the Targum understands of the Messiah.