If you do not take the place of being a sinner, and that under sentence of death and judgment, you step out of the place where God's mercy alone meets you, and where Christ has answered for you before God.
There is only one way out of that judgment; that is owning its justice, and accepting God's remedy through the death of His Son. Nothing else will do.
Some think their morality and religion will do. The answer for that is—for whom did Christ die? Do you find your remedy there? And how much are you going to add to God's remedy to make it complete? His remedy is, Christ has died for our sins and risen for our justification—nothing more or less. This changes everything when it is really believed.