It is suppose to be saying that being sinful makes it impossible for you to go to heaven. That because of the stain of sin you aren't allowed in God's presence.

The dumb part is it shows the owner of the vehicle doesn't understand their own theology as it has absolutely nothing to do with sin and all about relequeshing ones self to a god. You can sin all you want and as long as you believe (and possibly do works) you get in. It's why the religion is morally bankrupt. A repentant serial killer goes to heaven while a kind and generous atheist goes to hell.