In a world that judged wisdom as the maximum, to call someone a fool was almost an insult. For Christians to act according to the foolishness of the world, however, was the last straw.
Are you so foolish? Although you began with the Spirit, are you now trying to finish by human effort?
Galatians 3:3 NET
Behind the verse is the great contrast Spirit/flesh. The Galatian Christians were being led to adopt a greater religiosity, following the teachers who insisted on observing the law of Moses. But Paul describes this religiosity as carnality, based on human effort, bound to fail, falling under the divine curse.
We started in the gospel by faith in Christ. Let us continue in that faith. From faith to faithfulness. For in it is our spiritual inheritance.