Christianity is supposed to be a ‘system’ so simple that any child can grasp it:
“Jesus died for you; believe this and you will go to heaven. You will also be transformed so God will continually be accomplishing his will in you and through you.”
It’s supposed to be as simple as ‘surrendering’ your will to God’s will.
But if it is that simple, why are there organizations with big budgets, enormous buildings and highly structured ‘Christian education’ programs to explain how to do Christianity right? And why is there a multi-billion-dollar market for Christian books other than the Bible if the Bible contains all the knowledge you need?
Some of the Christian authority figures I encountered as a teenager and a young adult might have answered this challenge by explaining that salvation from hell is simple and immediate but salvation from sin is difficult and ongoing – that in fact it is never finished and may even become more difficult over time.
In any case, the church is in no position to criticize nonbelievers for rejecting its ‘simple’ message when there is a gigantic industry dedicated to explaining that message.