If we use the Lord's method on some present day religious practice, we would be no more unkind or un-Christian than was our Lord. They must expose and condemn the false religions about them in plain language. They must reprove, rebuke, exhort with all longsuffering and teaching to turn people to the truth. We must not fellowship error. The apostle Paul stated that error will eat as canker or gangrene.
False doctrine grows worse and worse and eats away the soul as gangrene eats away the flesh.
Those who put all emphasis on moral living and none on true doctrine would like to think that Paul had in mind some ugly immoral practice. However, in this instance he had reference only to doctrine. Those who say it matters not what one believes as long as he lives right are absolutely mistaken. It makes a difference whether it is Scriptural or not. Another thing we should notice is that both the teacher and the followers are rejected.