Unless the public sin of a believer is dealt with publicly, people will think the church does not take sin seriously and therefore gives tacit approval of it. A church that does not discipline sinning members (including the most prominent members) loses its credibility, because it does not take seriously its own doctrines and standards. A child who is not disciplined when he does wrong soon concludes that his parent’s standards are not really very important, because they are not enforced.
John MacArthur