It sounds reasonable: if what really counts is how you treat people, shouldn't sincerity and decency be enough? Why should the specific content of your beliefs matter, as long as you're kind?
What do we mean by “good”?
Compared to a murderer, most people look good. But that's not the standard the Bible uses. The standard is perfect love for God and perfect love for others, in every thought as well as every action (Matthew 22:37-39) — not "better than average." Jesus raised the bar further than most people are comfortable with: anger counts as murder in the heart, lust counts as adultery in the heart (Matthew 5:21-22, 27-28). By that standard —God's standard, not a curve against everyone else — nobody qualifies.
"For all have sinned, and come short of the glory of God."Romans 3:23
Why trust matters in Christianity
This isn't God being petty about ticking the right theological box. It's that salvation was never meant to be earned by good behaviour in the first place.
"Not by works of righteousness which we have done, but according to his mercy he saved us."Titus 3:5
If it's a gift, the way you receive a gift is by trusting the giver — not by proving you deserve it. Trying to earn your way to God through good behaviour, while refusing to trust what Christ already did, isn't a neutral, harmless alternative. It's the very thing the Bible calls sin at its root: self-reliance instead of trusting God.
Grace is not a reward for the deserving
"But we are all as an unclean thing, and all our righteousnesses are as filthy rags."Isaiah 64:6
That's not a comment on obviously bad people — it's a comment on our best moments, the ones we're proudest of. If even those aren't enough to bridge the gap, then no amount of "good person" behaviour ever could be.
Good works still have a place
None of this means how you live is irrelevant — it matters enormously, as the natural fruit of real faith (Ephesians 2:10). It just was never the way in. Good works are the response to being saved, not the method of earning it.