Isa 42:9  Behold, the former things have come to pass, and new things I now declare; before they spring forth I tell you of them.” 

Isaiah is often claimed as evidence for God’s omniscience of all future events. God declares the things that will happen before they happen. Barnes writes:

The phrase literally means, ‘before they begin to germinate,’ that is, before there are any indications of life, or growth in the plant. The sense is, that God predicted the future events before there was anything by which it might be inferred that such occurrences would take place. It was not done by mere sagacity – as men like Burke and Canning may sometimes predict future events with great probability by marking certain political indications or developments. God did this when there were no such indications, and when it must have been done by mere omniscience. In this respect, all his predictions differ from the conjectures of man, and from all the reasonings which are founded on mere sagacity.

In Barnes’ mind, Isaiah is about God predicting events that God could not possibly know because no current evidence exists for predicting that events. But this is not at all what the verses is about. The verse in Isaiah 42 is specific. God has told Israel a specific thing that He will do in the future:

Isa 42:6  “I am the LORD; I have called you in righteousness; I will take you by the hand and keep you; I will give you as a covenant for the people, a light for the nations, 
Isa 42:7  to open the eyes that are blind, to bring out the prisoners from the dungeon, from the prison those who sit in darkness. 

Barnes takes a straightforward verse about God telling His plans and turns it into a prooftext on Omniscience. That is just not what the text is about.