What separates an unbeliever from a believer?
That presumably talks about God but let's start with something simpler.
Let's say, you don't believe in homeschooling.
Because homeschooling exists, the gap is in your view of its merits. You don't believe in homeschooling as an adequate choice for the process of schooling. It lacks something that you equate with right schooling.
Can you precisely argue that something?
Back to God.
If you believe He exists but He's not for you, the gap is in your view of His merits. You don't believe God as an adequate choice for the process of your faith. He lacks something that you equate with right faith.
Can you precisely argue what He lacks?
If you believe He doesn't exist, the gap is in your view of Him as Creator. You don't believe God as Creator is an adequate choice for the process of explaining our origins. God as Creator lacks something that you equate with right explanation of origin.
Can you precisely argue how He is surely not our Creator?
In an unbeliever's argument, God is either lacking or nonexistent.
Tomorrow: Protecting the turf of the unbeliever.