Albert Barnes Commentary Isaiah 48:6

"Thou hast heard it; behold all this; and ye, will ye not declare it? I have showed thee new things from this time, even hidden things, which thou hast not known." — Isaiah 48:6 (ASV)

You have heard – You are witnesses that the prediction was uttered long before it was fulfilled.

See all this – See how it is all fulfilled. Bear witness that the event is as it was predicted.

And will you not declare it? – Will you not bear witness to the entire fulfillment of the prophecy? God appeals to them as qualified to testify that what he had declared had come to pass, and calls on them to make this known as a demonstration that he alone was God (see the notes at Isaiah 44:8).

I have shown you new things from this time – From this time I make known something which has not occurred before, so that you may have a similar demonstration that Yahweh is God. The new thing here referred to is, doubtless, the prediction of the deliverance from the captivity at Babylon – a new thing, in contradistinction to those which had been predicted before, and which were already fulfilled (see the notes at Isaiah 42:9; Isaiah 43:19).

Even hidden things – Events which are so concealed that they could not be conjectured by any political sagacity, or by any contemplation of mere natural causes. They are, as it were, laid up in dark treasurehouses , and they can be known only by him to whom the darkness shineth as the day, and to whom the night and the day are both alike (Psalms 139:12).