The law used to be God’s truth, but now it is grace, so to go back to the law as the Galatians had done is to disobey the truth (3:1). But grace is more than just a gospel to believe to be saved. It is an entire program that tells us how to live now that we’re saved, found in Paul’s epistles, that we’re to stand in (Rom.5:1,2). They had fallen for the law instead.
The law was the gospel the Jews had to believe to be saved, but it was also an entire program to tell them how to live once they were saved, one that said God would bless them with material blessings if they obeyed Him (Lev.26; Deut.28). That’s 180 degrees opposite of grace, that says God has al-ready blessed us with spiritual blessings in Christ (Eph.1:3) and then asks us to walk worthy of Him (Col.1:10). God is not blessing His people materially today, so falling for the law will make you think God doesn’t keep His promises.
The Galatians fell for the law because someone “bewitched” them (3:1). Simon bewitched people by giving out that he was some great one (Acts 8:9,11), and some allegedly great one had no doubt bewitched the Galatians the same way.
Paul was crucified with Christ (Gal.2:20) by being identified with Him in His death (Rom.6:3,4), and that’s how He’d been evidently set forth crucified among the Galatians too (3:1). But evidence is proof (cf.Jer.32:11), so where’s the proof that was “set forth” before the “eyes” of the Galatians that they’d been crucified with Christ? Well, Galatians 3:5 says God ministered the Spirit to them (cf.IThes.4:8) and worked miracles among them by the Spirit (cf.ICor.12:7-10). That’s what gave them visual evidence they’d been saved and crucified with Christ, just as it was “manifest” that the Corinthians had the Spirit (ICor.12:7-10).
Paul asked those Gentile Galatians if they received the Spirit after doing the works of the law awhile, or right away after they heard the gospel and put their faith in Christ (3:2), knowing they’d have to admit that they’d received the Spirit and His gifts right away, like the Gentiles in Acts 10:44.
Paul calls the law “the flesh” (3:3) because the law is heresy under grace, and heresy is a work of the flesh (Gal.5:19-21), our religious flesh. Going back to the law satisfies a believer’s religious flesh, but it’s a “voluntary humility” that God didn’t ask for (Col.2:18,20-23) and rejects.
The legalists told the Galatians the law would “perfect” their faith (3:3), but Paul says preaching Christ does (Col.1:27, 28). But not like the 12 preached him! They preached the law! Only preaching Christ according to the mystery perfects us (Rom.16:25); according to grace, not law (Rom.6:15)!
The Galatians immediately began to be persecuted when they started preaching grace (cf.Gal.5:11), and Paul reminds them if they go back to the law, they’ll have suffered that in vain (3:4)—“if it be yet in vain.” That is, if it wasn’t too late; and it wasn’t! If it were, he wouldn’t bother to write them.
The Corinthians prove men didn’t receive the Spirit and His gifts in those days by the law (Gal.3:5), for they were carnally living in sin, not living by the law, yet they came behind in no spiritual gift (ICor.1:7).
The other way Simon bewitched those people was by sorceries (Acts 8:9-11). Satan used sorceries to bewitch people back then because he always imitates what God does, and God was working miracles then. But today, God is teaching doctrines, so Satan has men teaching “doctrines of devils” (ITim.4:1)—like commanding to abstain from certain meats (v.3). That’s the law! Today, the law is a doctrine of devils. Just as God’s serpent (Num.21:6-8) became Satan’s serpent (II Kings 18:4) once God stopped using it to save people, so God’s law became Satan’s once God stopped using it to save people eternally. See how important rightly dividing is?