The prophet Isaiah is saying the same thing in more detail as what Peter says in Acts 3:19: "Repent." That is how the breach, the separation, between God and man will be healed. That is how atonement is made. Atonement is not all something that Christ does. There will never be oneness with God until man does something with his free-moral agency.
The problem in Isaiah 1 is a hypocritical people just going through the motions. They were observing the rituals: burning incense, making the sacrifices. Yet, at the same time, their daily lives were filled with all kinds of unlawful acts—business shenanigans—that, according to God's law, is taking advantage of others. They were lying about the weights and balances, selling shoddy products, and as a rule, not conducting business in an upright way. They were murdering one another's reputations through gossip, and lying to one another using charm and deceit. God is saying that their lives were full of hypocrisy.
In the same way, people who today claim to be children of God, who attend Sabbath services and holy days yet have a heart full of greed, covetousness, anger, hatred, bitterness, envy, and so on, are simply hypocrites.
As it pertains to us, what we see in Isaiah is that there must be a relationship between worshipping God and our character in its practical aspect out on the streets, in our homes, in the way that we conduct business. We might say our character away from church, out of the eyesight of God's people, must reflect what we profess to believe. How can those who treat their fellows with contempt, greed, envy, jealousy, anger, hatred, and revenge, do those things through the week and then come to church services before God, thinking that somehow or another they are not separated from Him? Jesus says in Matthew 5:23-24, "If you bring your gift to the altar, and there remember that your brother has something against you, leave your gift there before the altar, and go your way. First be reconciled to your brother, and then come and offer your gift." That is quite plain.
Because of all these things, God treated His people Israel in the same way as pagan idols treated their worshippers. Remember, the idols are not alive; they do not have ears that can hear, eyes that can see, or mouths that enable them to speak. So idol worshippers made their lamentations, their prayers, and their praises to their idols, and the idol never responded. God says, "I am going to be just like an idol to you. When you talk to me, I am not going to talk to you, and when you look at me, I am not going to look back at you. I am not going to see you." So in this way, He became as one who is dumb and deaf. He did not respond to their prayers.
It is essential to note that God, in His wisdom, knew before creating mankind that mankind would sin. If there were to be both reconciliation and character building, He would have to provide a means that would not only satisfy the legal requirements, but also contain within it the moral and spiritual influences that would motivate a man to cooperate on his own.
We play a major part in this because God has given us free-moral agency. By and large, the Protestant world has convinced Americans, Canadians, and Western Europeans that Christ did it all for us. It is a bald-faced lie! But sometimes, we who know better act as though it all depended on God. God gave us free-moral agency so that we can respond to Him, put His Word into practice, and exemplify before others what God is like.
It would be nice to say that we live lives like Christ so much that we could say of ourselves what Christ said: "If you have seen me, you have seen the Father" (John 14:9). There is a Person who was really at one with God.
What God is trying to do with the things that He has provided—namely, the life, death, and resurrection of Jesus Christ and the gift of His Holy Spirit—is to motivate man to repent—to change, to turn to God, to resist the desire to continue in sin—to work at building character and learn to live by faith.