Righteousness Imputed

How is God’s message through Isaiah a two-fold message of warning to those who are not God’s chosen and of assurance to His own? How is the LORD comforting His servants here? Can anyone be righteous outside of God making them so? If you transgress one time in any way are you guilty of every law? What was the point of Cain murdering Abel? Why don’t depraved sinners rejoice that Christ has accomplished all that was needed for salvation? How do some worship God in vain? What does imputed mean according to this Word?