God demands we live ethically. But what about those times when we don't? The most vital issue Christianity answers is "How can we be right with God when we are not thoroughly good?"
There is profound misunderstanding on this point. Part of the confusion is because many err in defining goodness according to human standards. God, on this view, is concerned with what kind of individual one is "on average." If the good outweighs the bad—if good is predominant—then God winks at the occasional moral lapse.
But justice never works like that, does it? The law demands that each person obey every law always, not most laws usually. You can be an upstanding citizen all your life, but one single crime is still going to bring you before the court.
Further—and this is absolutely critical—no amount of good behavior pays for bad behavior. Period. Law requires consistent obedience, and that which is already owed cannot be used to pay for past errors.
God, like all lawgivers, requires nothing less than moral perfection. "But that's impossible," you say. You're right. That's why we need a Savior. That’s how we can be right with God when we’re not thoroughly good.