Only the children of the Free Woman inherit; the slave and her children were cast out. So argued Paul previously. Now, he builds on the idea of being free.
There was no "blending" of Law and Gospel. Accept one and be "cut off" from the other. It is altogether possible to be "cut off" from Christ, and "fall from grace." Choices make a big difference!
If choices matter, then it also matters to obtain accurate, and adequate, information. Clearly, there was among the Galatian Christians an instigator of departure. Notice Paul's emphasis on "faith" (vv. 5, 6); but this feller was "troubling" them. He was promoting flawed information.
They had been "running well"; but now they were not "obeying" the truth, they were hindered, and they were falsely persuaded (vv. 7, 8). This persuasion was NOT from Jesus. That's why they were in danger! And, that's why he would bear his punishment (v. 10).
Best response: Stand firm (v. 1), and let the false teachers be "cut off" (v.12).
Join us Friday; we'll talk about these things.