Why can't Satan or the world get to a believer who is hidden with Christ in God?
The believer is secure because God Himself has hidden their new life with Christ in God. If the Creator hides something, no one but Him can find it. The walnut illustration shows that protective hiding: Satan and the world cannot reach or touch those thus hidden.
Les explains that Paul says believers are dead to those things, and the new eternal life imputed to us is hid. Les emphasizes that if the God who created this universe hides something, no one but Him will ever find it. He hides us with Christ and in God. Using the walnut, Les illustrates the outer shell, then the tough shell, and then the meat down in the crevices, where no one but God can find it. Therefore Satan cannot get at us there, the world cannot get at us there, and no one can touch us. This is assurance and a promise, even though Les admits he does not feel an outer covering and is just as vulnerable.