The feast of the Triumph of the Cross is Thursday, Sept. 14. How should we celebrate it? There's a curious statement of St. Paul's that, if we understand it correctly, shows us the best way. He says: "In my flesh I am filling up what is lacking in the afflictions of Christ on behalf of His body, which is the Church" (Colossians 1:24).

What could that possibly mean?

St. Augustine provides a brilliant answer. He explains that if Christ is our head and we're members of His body, then all of His sufferings belong to us and all of our sufferings ultimately belong to Him. "If then you are among the members of Christ ... your sufferings are added because they were lacking. You fill up a measure ... you suffer as much as needed to be added from your sufferings to the total suffering of Christ, who suffered as our head and suffers in His members."

So often we're tempted to make our relationship with Christ into a zero-sum game: Whatever is accomplished by His grace isn't accomplished by our effort; whatever is attributed to our suffering is taken away from His. But it isn't like that. Jesus doesn't compete with us. His grace empowers our effort; our sufferings are joined to His. It isn't Christ or us at work, it's Christ in us at work.

Think of it this way: Jesus not only accomplished something on the cross, He also revealed the law of the cross. And, no less than the law of gravity, the law of the cross was written into the universe from the foundation of the world.

Just as gravity was at work before Newton discovered it, so the law of the cross was at work before Jesus revealed it. Consider the Old Testament episode of the serpent mounted on the pole: Whoever looked on it with faith was saved. This foreshadowed the law of the cross, and Jesus confirmed the link when He said: "And just as Moses lifted up the serpent in the desert, so must the Son of Man be lifted up, so that everyone who believes in Him may have eternal life."

And, as with gravity, the more we understand how the law of the cross works the more we can use it to shape our actions. For example: We're often tempted to criticize the sinful world from the sidelines and somehow expect that to make things better. But that isn't how the law of the cross works. Jesus didn't just sit back and criticize the sinful world from the sidelines. He got involved. He stepped into the situation. He made reparation in His own body for the sins of the world. That cost Him something. But it worked: By His sacrifice, He opened up a path for sinners to enter into heaven.

Are we willing to do the same — not only to avoid sin, but also to make reparation in our lives for the sins of others? We can, you know. Because we're members of Christ's body, His power overflows to us. We can let the power of his cross work in us, and we can add our sufferings to the work of His body.

In that sense we can fill up in our bodies something that's needed in the Body of Christ. When we do that, Jesus works in us to open a path for sinners to enter heaven. That's the triumph of the cross at work in our lives. That's the best way to celebrate the feast.