How does a person grow and change? How do people understand the truths of the gospel while still in their sinful state? It's a mystery. Just as we know not how a seed grows and sprouts into a plant, we also do not know exactly how the kingdom of God grows and sprouts in the hearts of God's people.
"And he said, 'The kingdom of God is as if a man should scatter seed on the ground. He sleeps and rises night and day, and the seed sprouts and grows; he knows not how.'"Mark 4:26-27