17. They--your flatterers: in contrast to Paul himself, who tells them the truth.
      zealously--zeal in proselytism was characteristic especially of the Jews, and so of Judaizers (Ga 1:14; Mt 23:15; Ro 10:2).
      affect you--that is, court you (2Co 11:2).
      not well--not in a good way, or for a good end. Neither the cause of their zealous courting of you, nor the manner, is what it ought to be.
      they would exclude you--"They wish to shut you out" from the kingdom of God (that is, they wish to persuade you that as uncircumcised Gentiles, you are shut out from it), "that ye may zealously court them," that is, become circumcised, as zealous followers of themselves. ALFORD explains it, that their wish was to shut out the Galatians from the general community, and attract them as a separate clique to their own party. So the English word "exclusive," is used.

JFB.