It's impossible to be good apart from Christ because Christ is the definition of what is good.
When we as believers talk about being good we're not just making stuff up.
Good is not arbitrary.
It's not what you want to be good.
It's not what I want to be good.
It's what God says is good.
And God's standard of good is Jesus Christ.
He's the standard of what's true and false. "See to it that no one takes you captive through philosophy and empty deception, according to the tradition of men, according to the elementary principles of the world, rather than according to Christ." (Col.2:8)
And he's the standard of what's right and wrong. It's interesting to note how often Paul, in forbidding certain behaviors, will say that reason those behaviors are not acceptable because they are not 'according to Christ.' Just check out Colossians 3.
Why do certain things need to be put off? They are earthly and not according to Christ.
Why do certain things need to be put on? They are the kinds of practices that are in accordance with Christ.
Christ is the standard.
The unbeliever, in rejecting Christ, has rejected the standard of what is good.
Sometimes they do that blatantly.
They reject all absolutes...which leaves them in a difficult position if they claim they are good people, because how you can be a good person when you have rejected the standard of what is good. The person who rejects the external standard of what is good, God's Word, only has his opinion about what is good. If he believes in good at all, he makes decisions about good and evil on the basis of what he feels in his gut, or what he's heard, or what he's read.
He rejects Christ as the standard and sets himself up in his place...which might feel good, but doesn't fly because it's not reality.
Saying that you are a good person on the basis of what you think is good is like going into a grocery store and picking up a bottle of milk and saying I believe this bottle of mik is free. Just holding the milk bottle above your head walking through the store shouting out that you believe the bottle of milk is free, probably won't do you much good. If the clerk doesn't toss you out the store, at the very least he'll tell you that while it's nice you think it's free, you are not the one who gets to decide.
Ultimately Christ and His Word are the standard of right and wrong. We can go around saying otherwise but when we do, we are ignoring the way things really are. If we have substituted our standard of what is good and what is not good for God's standard of what is good, we're going to be very disappointed when we face Him on judgment day.
You can imagine a criminal going before a judge and when asked his defense, responds "I don't think murder is wrong." To which the judge replies, "But the law says it is." The criminal becomes indignant and replies, "I don't think so." To which the judge replies, "Bailiff...take this man away." The criminal may have his opinion about the law, but it won't stand in court.
Yet that's what those who are trusting in their own goodness while rejecting Christ are planning on doing when they stand before God one day. They've rejected God's standard and replaced it with their own and think he's going to accept.
When someone says to you they are a good person, you might ask "Why do you say that?"
If they are merely resting in their own opinion of what is good, when they call themselves a good person, they are saying something completely meaningless.
Imagine a person who picks up a book and says I feel like this weighs two pounds. Then another person picks it up and says no I feel like it weights forty pounds. Then another person picks it up and says I feel like it weighs nothing at all.
Those statements don't mean much. It doesn't really matter what any of them feels the book weighs. It matters what it weighs. If you've rejected the scale, you have nothing left but a whole bunch of basically meaningless statements.
Once you throw the scale out trying to weigh things is pretty silly.
Sometimes people aren't quite that bold however. They are religious and they believe in absolutes, they just don't think Christ is the absolute.
You look at many world religions and they'll say compassion is important, they'll emphasize the importance of love. And so there are many who will say, the important thing is that we are compassionate and loving. How could God possibly say that what they are doing isn't good if what they are doing is in accordance with the kinds of actions the Bible describes?
That's a good question isn't it?
If I'm doing what Christ says is good, why isn't that enough?
That'll have to wait until tomorrow...