Paul addresses the foolishness of abandoning the grace connection with God through His Holy Spirit for a “fleshly” works relationship. It’s always tempting for Christians to default to a works relationship with God. But it is indeed “foolish.” It only brought us great suffering before, why do we think it will be different now. Paul writes in Galatians 3:3-5, “Are you so foolish? Having begun by the Spirit, are you now being perfected by the 
flesh? Did you suffer so many things in vain—if indeed it was in vain? Does he who supplies the Spirit to you and works miracles among you do so by works of the law, or by hearing with faith?” The point is that we just kill ourselves when we abandon grace and focus on works of the law as the basis of our relationship with God. Through the Spirit we’re connected to God through Christ’s righteousness not our own! We are so foolish to abandon grace for law. The law fails us and we end up starving for communion with God that we once had in the Spirit.
When we lived in Dallas some years ago fire ants had moved into the area. At that time they had virtually taken over the southern United States since they were accidentally transported here a few decades ago. They are amazingly adaptable, fiercely aggressive, and multiply seemingly overnight. Worst of all, insecticide sprays generally can’t destroy the mound’s inhabitants. Like a mighty army they have marched in, impervious to brute force. Scientists have now found a rather crafty way to wipe out whole colonies. Pellets of the ants’ favorite food are tainted with a special tasteless, odorless poison and sprinkled around the mound. The worker ants immediately begin gathering up the tainted treasure and take it down into the heart of the colony. Then they unwittingly feed the poisoned pellets to their queen, slowly killing her! When the queen dies, no more workers are produced, and so in a couple of weeks the entire colony starves to death. How ironic! Food that looked so good caused their starvation.
That is how it is with false doctrine, especially the false doctrine of salvation by works or salvation by Grace plus works. It’s deadly and eats away at the heart of the Christian message until it has wiped out every semblance of the fruits of the Spirit: love, joy, peace, etc. The foolishness of the Galatians again refers to those who don’t “think” their way through the implications of this false doctrine. Paul says they lack discernment. Those who lack discernment import it, this false doctrine, into their hearts and it will work its way into the heart of the church, thinking it is harmless and in fact quite good. If any wise “ant” smells the poison and protests, he is ridiculed! And in the end the next generation starves to death spiritually. We will never earn God’s acceptance by being good! We can only receive God’s acceptance through faith in Christ. While filling our bellies with good deeds and holy effort we actually starve to death. Our hunger and thirst for God’s righteousness will never be filled by keeping the law, but it can be filled by God’s grace through faith in Christ.