This is the message we have heard from him and declare to you: God is light; in him there is no darkness at all. If we claim to have fellowship with him and yet walk in the darkness, we lie and do not live out the truth. But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, his Son, purifies us from all sin (1 John 1:5–7).

Set Theory is a system of organizing information into groups (or “sets”) to discover if and how the contents of one set overlaps with the contents of another. 

For example, if SET A contains only even numbers, and Set B contains only odd numbers, how much overlap will there be between the sets? ZERO! NO overlap. NO compatibility. NO common ground. In Set Theory, this outcome is represented by two brackets with NOTHING between them and looks like this: 

{ }

It’s called the EMPTY SET. 

This long-ago high school math/logic exercise began swirling around my brain as I read this week’s passage from 1 John, where the apostle poses the ultimate compatibility challenge to Christians, which might be expressed in the following equation: 

{GOD} ∩ {CHRISTIANS} = ?

You can read that strange symbol (∩) to mean “How much OVERLAP is there between God and the folks who profess to walk with Him?” (It’s a question worthy of our consideration.)

John begins the process by naming one of God’s salient characteristics: 

“God is light; in him there is no darkness at all.”

Since LIGHT and DARKNESS are incompatible, with no OVERLAP, the equation results in the EMPTY SET. 

{light} ∩ {darkness} = { }

Next, John addresses those who say they have fellowship with God yet walk in darkness. As you might expect, based on our previous equation, the impossibility of such a claim nets the very same outcome. 

{fellowship with God} ∩ {walk in darkness} = { }

As an exercise in Set Theory, it’s clear that those who walk in darkness yet claim to have fellowship with God do not have a leg to stand on, since walking in darkness is totally incompatible with the God who is light. And those who deceive themselves through such baseless lies not only produce the EMPTY SET, but reveal the SPIRITUAL EMPTINESS of their EMPTY LIVES. 

In verse 7, John offers a corrective that promises lives more compatible with God:

But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, his Son, purifies us from all sin.

Stepping out of the darkness and confessing our sins changes the equation so our lives OVERLAP with the ONE we claim to follow, as he FORGIVES our sin, and restores our FELLOWSHIP with Him and with one another. It looks like this:

{God is light} ∩ {walk in the light} = 

{fellowship and forgiveness}

This new equation fulfills the apostle’s desire for all believers: 

“…that your joy may be full” (1 John 1:4, KJV).

Abundant joy comes from delighting in the Lord, walking in His Light, and living in conformity to the example of Jesus the Messiah.

It’s a winning formula for a life that’s FULL. 

Not EMPTY.

Abba, teach us to delight in your light and walk in your ways so our lives may be full of joy!