1 Corinthians 5:6-11

Your boasting [over the supposed spirituality of your church] is not good [indeed, it is vulgar and inappropriate]. Do you not know that [just] a little leaven ferments the whole batch [of dough, just as a little sin corrupts a person or an entire church]? Clean out the old leaven so that you may be a new batch, just as you are, still unleavened. For Christ our Passover Lamb has been sacrificed. Therefore, let us celebrate the feast, not with old leaven, nor with leaven of vice and malice and wickedness, but with the unleavened bread of sincerity and [untainted] truth. [Ex 12:19; 13:7; Deut 16:3] I wrote you in my [previous] letter not to associate with [sexually] immoral people— not meaning the immoral people of this world, or the greedy ones and swindlers, or idolaters, for then you would have to get out of the world and human society altogether! But actually, I have written to you not to associate with any so-called [Christian] brother if he is sexually immoral or greedy, or is an idolater [devoted to anything that takes the place of God], or is a reviler [who insults or slanders or otherwise verbally abuses others], or is a drunkard or a swindler—you must not so much as eat with such a person. [2 Thess 3:6]