That's what I thought as well. But I think it's a misconception. It's a common teaching that sin is a separation from God, however that's not quite accurate. As being created by God, it is not in our nature to exist without him. If we were to separate from his presence, we would revert to non-existence for God created us out of non existence. Rather sin is like "missing the mark". Imagine if you were playing darts, your aim should be for the center, and when you don't quite get that mark in the center is exactly what sin is. The mark or center is perfection, it is God. Those who end up in heaven or hell really depend on this small aspect, what are you aiming for? when we choose not to aim for the center we are choosing hell, however when we choose to aim for the center yet still miss anyway, we are choosing heaven and in that scenario God will grant his grace that you may keep getting closer and closer to the center. Salvation and heaven isn't about chilling up in the clouds and doing nothing. It's a continuation of that trying to hit the mark. It takes eternity to become one with God.