Galatians 5:7 - You were running well; who hindered you from obeying the truth?
These words are clear. Paul declares that he taught correctly before and is teaching correctly now; at the same time he suggests rather subtly that the Galatians had been running correctly before, that is, had obeyed the truth and had believed and lived correctly, but that they were not doing so now, after they have been led astray by the false apostles. Moreover, he uses a new expression here when he calls the Christian life a “running.” To the Hebrews running or walking means living or behaving. Teachers and learners “run” when the former teach purely and the latter receive the Word with joy (Matt. 13:20) and when the fruits of the Spirit follow in both. This is what happened while Paul was present, as he testified in chapters three and four as well as here, when he says: “You were running well; that is, you were living a good life and pursuing the right course toward eternal life, which the Word promised you.”
But the words “You were running well” contain comfort. For with these words Paul pays attention to the trial by which the devout are disciplined; to themselves their life seems dreary, closer to crawling than to running. But when there is sound teaching—which cannot be without results, since it brings the Holy Spirit and His gifts—the life of the devout is strenuous running, even though it may seem to be crawling. To us, of course, it seems that everything is moving ahead slowly and with great difficulty; but what seems slow to us is rapid in the sight of God, and what hardly crawls for us runs swiftly for Him. Likewise, what is sorrow, sin, and death in our eyes is joy, righteousness, and life in the eyes of God, for the sake of Christ, through whom we are made perfect. Christ is holy, righteous, happy, etc., and there is nothing that He lacks; thus there is nothing that believers in Him lack either. Therefore Christians are really runners; whatever they do runs along and moves forward successfully, being advanced by the Spirit of Christ, who has nothing to do with slow enterprises.
Those who fall away from grace and faith to the Law and works are hindered in this running. This is what happened to the Galatians; they were persuaded and led astray by the false apostles, whom Paul attacks obliquely with the words “Who hindered you from obeying the truth?” He spoke the same way earlier (3:1): “Who has bewitched you so that you do not obey the truth?” Paul indicates here incidentally that men are so violently crazed by false teaching that they accept lies and heresies as truth and as spiritual teaching, while they swear that the sound teaching which they had loved originally is in error, but that their error is sound teaching; this position they defend with all their might. Thus the Galatians, who were running along very well at first, were led by the false apostles into the opinion that they had been in error and were moving along very slowly when they had followed Paul as their teacher. But later, when they had been led astray by the false apostles and were forsaking the truth completely, they were so bewitched by these false arguments that they believed their whole life was moving along and running very successfully. Today the same thing is happening to those who have been deceived by the fanatical spirits. This is why I am often wont to say that a fall from sound doctrine is not human but demonic, from the very heights of heaven to the lowest depths of hell. Men who persevere in error are so far away from acknowledging their sin that they even defend it as the height of righteousness. Therefore it is impossible for them to be forgiven.
Luther, M. (1999). Luther’s works, vol. 27: Lectures on Galatians, 1535, Chapters 5-6; 1519, Chapters 1-6. (J. J. Pelikan, H. C. Oswald, & H. T. Lehmann, Eds.) (Vol. 27, pp. 31–33). Saint Louis: Concordia Publishing House.