Albert Barnes Commentary Isaiah 48:5

"therefore I have declared it to thee from of old; before it came to pass I showed it thee; lest thou shouldest say, Mine idol hath done them, and my graven image, and my molten image, hath commanded them." — Isaiah 48:5 (ASV)

I have even from the beginning declared it to thee - He had foretold future events, so that they had abundant demonstration that he was the true God, and so that they could not be mistaken regarding the source of their deliverances from danger.

Mine idol hath done them - The idols and molten images had not foretold these events. Therefore, when they came to pass, it could not be pretended that idols had produced them. By predicting them, Yahweh kept up the proof that he was the true God, and demonstrated that he alone was worthy of their confidence and regard.