C.S. Lewis - The Screwtape Letters
“Cards are as good as murder, if cards to the trick.”
Meaning, the sin need not be spectacular, as long as Satan wins the soul.
No sin can go into heaven otherwise sin would overtake heaven and God will not have that. Even one sin, not dealt with, would keep one from heaven. That is why we need the Savior - The Lord Jesus Christ. And believing He died for all ones sins and following Him brings assurance of heaven. There is no other way.