Albert Barnes Commentary Isaiah 42:20

"Thou seest many things, but thou observest not; his ears are open, but he heareth not." — Isaiah 42:20 (ASV)

Seeing many things - That is, the people, the Jews, spoken of here as the servants of God. They had had an opportunity to observe many things pertaining to the law, the government, and the dealing of Yahweh. They had often witnessed His intervention in times of calamity, and He often rescued them from peril. They could not help but observe these things, even though they had chosen to disregard the lessons these events were designed to convey.

But thou observest not - You do not keep them (תשׁמר tı̂shmor); you do not regard them.

Opening the ears - You have your ears open. They heard the words of the law and the instructions conveyed by tradition from their fathers, but they did not lay them to heart or pay attention to them (see the note at Isaiah 6:10).