What is the modern equivalent of the circumcision requirement?
For believers today, the equivalent is any legalistic demand or extra requirement that people insist must be added to faith in the Gospel. It is not circumcision itself, but the various works or rituals that imply Christ's finished work was insufficient and that salvation requires something more than grace through faith.
Les explains that the Galatians were being tempted to return to legalism, which at that time centered on circumcision promoted by the Jews. But for us today, circumcision is not the criteria. Instead, the modern equivalent is any other thing people try to tell us we must do besides believing the Gospel. Salvation is all of grace by faith plus nothing else, and adding anything to it takes away from the finished work of the cross. Les emphasizes that we are not under the system of law or any legalistic demands for salvation; we simply believe that Christ did everything needed and that it is a finished transaction. Through Paul's writings, God assures us we stand justified, forgiven, sanctified, and glorified by faith in that finished work.