Paul had some idea of what was going on behind his back.  He was not a fool.  Nevertheless, Paul was shocked when he learned that the believers in Galatia had been seduced by these lies, rejecting the doctrine of grace that they had once so fervently embraced!  It was not lost to Paul that to reject the doctrine of grace is necessarily to reject the cross (Galatians 3:1).  The only reason eternal life is a free gift to us is because it was already paid for by the blood of Christ.  Grace is a necessary conclusion of the cross, and to deny the doctrine of grace is to ultimately deny the truth of our Lord's payment for sin at Calvary.

And when the eternal destiny of every man, woman and child on this planet hinges on the doctrine of grace, when the only hope of a lost sinner is to renounce any hope of salvation through obedience to the law and receive the free gift of eternal life through Jesus Christ, there can be no compromise.  Those who undermine this precious doctrine mislead men unto eternal damnation, and make themselves enemies of the cross!  But God brings life thought of death, and resurrection from the grave.  The tragedy of Galatia, the tragedy of genuine Christians renouncing the gospel of grace for "another gospel," gave birth to one of the most resounding triumphs in the history of the Christian Church.  For it was the apostasy of the believers of Galatia that drove Paul to pen the single greatest treatise on the doctrine of grace in all of Christian literature . . . The Epistle of St. Paul to the Churches of Galatia.