In my opinion, it is the blasphemy against the Holy Spirit that we have been warned about in Matthew 12:31. It seems to me to be not just worse than the original sin, but even worse than simply neglecting to accept Christ.
But while I dabble, I am not enough of a theologian to justify that point, and maybe it's something else.
You got it. God didn’t intend for just “theologians” to understand His word— just those with open and honest hearts who want to know the truth. The things the apostles wrote down were for all Christians to understand (1 John 2:1; etc.)