Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing.
Behold - i:e., mark what I say.
I Paul. However you disparage me, I give my personal authority as enough by itself to refute all opposition.
If ye be circumcised. - `if ye still suffer yourselves to be circumcised' (Present, peritemnesthe: implying continuance); namely, under the notion of its being necessary to justification (Galatians 5:4; Acts 15:1). Circumcision is not regarded simply by itself (for, viewed as a national rite, it was practiced for conciliation's sake by Paul himself, Acts 16:3), but as the symbol of Judaism and legalism. If this be necessary, then the Gospel of grace is at an end. If grace be the way of justification, then Judaism is not.
Christ shall profit you nothing (Galatians 2:21) - for righteousness of works and justification by faith cannot co-exist. 'He who is circumcised (for justification) is so as fearing the law; he who fears disbelieves the power of grace; and he who disbelieves can profit nothing by that grace which he disbelieves (Chrysostom).