Now we command you, brothers, in the name of our Lord Jesus Christ, that you withdraw yourselves from every brother who walks in rebellion, and not after the tradition which they received from us.
In the name of our Lord Jesus Christ ...  This is an appeal by the apostle to the authority of his commission and office as an apostle of Christ.  It should be noted that he did not fail to mention "in the name of our Lord Jesus Christ," thus making it clear that his command carried the full weight and authority of Christ himself.  As Mason pointed out: