Why is every rejection of the gospel making it harder for a person to eventually believe?

Each rejection reinforces rebellion and hardens the heart, so saying no becomes easier and recognizing God's mercy becomes harder. Over time, resistance builds barriers that make later belief increasingly difficult, and in old age such hardness can become almost impossible to break through, as with Pharaoh.

Les explains that when people are brought to a place of making up their mind for or against God and they say no, the next time it is easier for them to say no than it was the last time. Their whole concept of rebellion grows, while their concept of recognizing God's mercy gets smaller. As people get old and remain rebels against the grace of God, it is hard to break through—almost impossible—because they have become so hardened. Every time they are confronted with the choice of believing the gospel and reject it, it becomes that much harder at some future time to break down those barriers of resistance. And so it was with Pharaoh.

How does rejecting the gospel each time affect a person's ability to believe later?

Each rejection of the gospel hardens the person further. Saying no makes the next no easier, while recognition of God’s mercy shrinks and rebellion grows. Repeated refusals build barriers of resistance, so later belief becomes much harder; for one still rebelling against grace into old age, it is almost impossible to break through.