The problem in Isaiah 1 is a hypocritical people who are just going through the motions. They were going through the ritual as we can see: they were burning incense, they were making the sacrifices. But 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 balances and the scales; they were selling shoddy products; they were not conducting business in an upright way.
They were murdering one another through gossip; and lying to one another using charm and deceit. God is saying, "That's a bunch of folderol!"
For people to claim that they are the people of God, go through the ritual of attending Sabbath services, holy days, and yet have a heart that is full of greed, covetousness, anger, hatred, bitterness, envy, and on and on.
What we are seeing in Isaiah—as it pertains to us—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, away from services, out of the eyesight of God's people.
How can those who treat their fellows with contempt, greed, envy, jealousy, anger, hatred, revenge, do those things through the week and then come to services before God, thinking that somehow or another they are not separated from Him?
