What does God want from us?
We can never live up to the standards he requires of us. The only way for us to escape our just punishment is to accept God's mercy through the sacrifice of Jesus Christ. But having done that, what should we do? We have acknowledged God's authority over us. We want to obey him. But our sinful hearts make it impossible for us to obey and please God the way Jesus did. How are we supposed to deal with God after being saved when we know that we can't ever be what he wants us to be?
Context is important for this. We are not removed from God. He is not a legislator who sits far away and hands down stone tablets chiselled with arcane regulations. We are in a loving relationship with God. For Israel, the Mosaic law was a way to demonstrate and reinforce their commitment to that relationship. It was also a way to make Israel aware of their own perfidy and sinfulness, to make them realise that they had "the desire to do what is right, but not the ability to carry it out".
We wrong God. When we sin against him we wrong him, and that has consequences for our relationship. There is always more forgiveness - God's grace and love are infinite. But we can only come back into right relationship with God when we acknowledge that we are not there at the moment. If your best friend stays overnight and drinks all your milk, you will forgive them - but things will become much more fraught if they refuse to acknowledge that anything improper has occurred.
Consider the story Jesus told about the Pharisee and the tax collector: a man who held to every iota of the Mosaic law compared to one of the lowest classes of sinners in first-century Judea. But it is the sinner who goes home justified because he acknowledges he needs to be. The Pharisee thinks that his actions make him righteous, and he fails to see that like all human beings - save one - he has wronged God.
We can maintain a loving and close relationship with God despite the knowledge of our inability to properly obey him. But we have to remain active within that relationship. God is always reaching out to us, but we still have to reach back.