Religion is man powered, where Christianity is God powered.
God couldn't spell out how to get into heaven because the proud heart could follow it and get in. Instead His truth hides perfectly from the proud, he can only be found by the humble heart. The proud heart always draws the same conclusions from the bible, "what can this amazing person do to get in". The proud heart doesn't want to believe in replacing there goodness and greatness for Jesus's, because they believe they have so much of it themselves.
The thing with spiritual levels is like that of earthly:- You can't help the deaf by turning up the volume; you cant make a dark room bright by washing the walls; you need to turn on the light. We can't be righteous in God's eyes by trying to stop sinning:- we need to receive His righteousness and forgiveness like a seed which sets us free from the power of sin. :- Romans.
In the garden one tree the proud heart was attracted to and the other tree was for the humble heart. For imperfect humanity, what you achieve doesn't mater, it's all about the heart and what man wants. And when we finally stand before God and He asks us why we should come in, the proud will talk about how good they have been and the humble will say they believe in him.
The ass hols in there long robes have done a good job convincing the world that the tree of the knowledge of good and evil on the left is the right way to go. The law is a test of the heart to see weather we would choose grace or deeper into law. When the proud heart looks at the law it thinks "shit i think i can do this, since I'm so wonderful." The humble heart says i can't do this i need Jesus.