“Produce fruit in keeping with repentance.” -Matthew 3:8
After telling people to repent, John made sure to clarify that repentance (metanoia) is not a one-time act. You need to keep going with it.
Perhaps the Pharisees and Sadducees he was talking to had started out with repentance, but had given up on it. Maybe they thought they could produce fruit more effectively their own way. Or maybe, as John alludes to in verse 9, they had begun feeling justified by their heritage, and no longer felt their need for forgiveness.
Metanoia is not often a comfortable place to be. Living according to your faith instead of your immediate circumstances might put you in some scary situations. But worse than that, metanoia never lets you justify yourself. It is always accompanied by clear recognition of your sinfulness, and the resolution to do better.
But the great part is that the fruit we bear is not dependent on how justified we feel. Our fruit depends on how we depend on God. It depends on us “keeping with repentance.”
So don’t give up on it. Don’t harden your heart. Resist the urge to justify yourself. Never settle for a shallow answer to your hardest questions. Keep breaking down and building back up. Keep asking for forgiveness and being re-baptized by the Holy Spirit.
And your repentant life, even when you can’t understand it, will produce the fruit of better life–in you and the people around you.