The reason there is a crisis in Galatia is because the saints have given the time of day to a teacher or teachers they ought to have ignored. Paul brings this basic problem home to the Galatian believers in a very pointed way.
His fundamental argument, which he presses here, asks them how they received the Spirit. How did the Spirit work among them? Why are they even thinking about changing to “another way?” Paul’s fundamental assumption here is that we live like Christians in the same way that we became Christians. We receive the Spirit by faith. What makes us think that we are to retain the Spirit by any other means than this same faith?
A very common and dangerous assumption among Christians is that “true” Christians cannot be enticed by heresy. Now it is true that the elect will persevere to the end, and they will continue to hear the shepherd’s voice, but it not true that this all happens with them coasting easily down hill into glory.
In the case of the Galatians, Paul had to (verbally) slap them around—they were entertaining very dangerous opinions, and they thought that they had every right to do this. So Paul calls them foolish Christians. He says their behavior could be accounted for if he postulated some kind of wizard casting spells on them. This is the nature of life prior to the resurrection; we should never forget that the Church contains many Christians capable of acting very foolishly. And there are even times when the sin is worse within the Church than outside.
Paul is warning them against the “deeper walk trap.” Despite how clearly Paul has spoken on the subject here, a persistent error in the Church says that yes, you come to Jesus by grace through faith. But then, if you really want to “enter in” the deeper life, or the higher life, or the special life, you must do something else, of another nature. That something else might be speaking in tongues, receiving a mystic vision, or memorizing the Shorter Catechism. But the Scriptures teach us that we are to continue to walk in the same way we began to walk, which is by grace through faith. We have this passage; we continue the same, identical way we began. Paul also says in Colossians 2:6, “As ye have therefore received Christ Jesus the Lord, so walk ye in him.” By grace through faith, from first to last. Faith alone, faith always.
Paul is clearly arguing his case. But as with everything else, an argument like this can only be followed in the power of the Spirit. First, he says, did you receive the Spirit by hearing with faith or by works of the law? (But the subtext here is that they could only receive Paul’ argument by faith.) Paul then assumes that their behavior answers the question wrong. “Are you so foolish?” he says (v. 3). If you couldn’t start without the Spirit’s work, what makes you think you can run without the Spirit’s work? If you cannot take the first step of the marathon without the Holy Spirit, why do you want to run the marathon without the Spirit? (Subtext: if you cannot begin without the Spirit, how can you read my argument here in Galatians without the Spirit?) Their behavior is throwing away so much good—making their previous suffering a vanity (v. 4). He states the argument again another way. What about all the miracles the Spirit has performed in your midst? Did He do that because you all were circumcised? Or because of your faith?
The carnal man does not understand the things of the Spirit because they are spiritually discerned “But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned” (1 Cor. 2:14). We declare, we preach, we argue, we write, we plead, we point. This is just another way of saying we plow, we plant, we weed, we hoe, we water—but only God gives the increase. Believe in God, therefore, and in His Son, Jesus Christ, in the power of the Holy Spirit.