Albert Barnes Commentary Isaiah 41:3

"He pursueth them, and passeth on safely, even by a way that he had not gone with his feet." — Isaiah 41:3 (ASV)

He pursued them – When they were driven away. He continued to follow, and consigned them to defeat and ruin.

And passed safely – The marginal note, following the Hebrew, reads, ‘In peace.’ This means he followed them uninjured; they had no power to rally, he was not led into an ambush, and he was safe as far as he chose to pursue them.

Even by the way that he had not gone with his feet – This refers to a route he was not accustomed to marching; an unusual journey; in a land of strangers.

Cyrus had spent his early years east of the Euphrates. In his conquests, he crossed that river and extended his march beyond even the Halys River to the western extremity of Asia, and even to Egypt and the Red Sea.

The idea here is that he had not traveled in these regions until he did so for purposes of conquest – an idea that is strictly in accordance with the truth of history.