Under the Torah (Law) of the Old Covenant, filth was considered something that would be infect the entire body. If a mad touched but a speck of blood, then he was unclean and must go through ritual cleansing. Even Passover was put off until a person could be made clean. They did this so as to make sure that they were entirely clean and holy before a God Who is always Holy. Before Passover (the Feast of the Unleavened Bread), good Jews still to this day go through their home and clean ever nook and cranny in order to clear out the yeast (leaven) or their Passover is corrupted. When Joshua was marching on his conquest of Palestine, he lost a battle that should not have been lost. Why? Because there was ONE member of the camp, out of hundreds of thousands, that had brought sin in.
It seems to me that at times even the greatest and most noblest of organizations can fall and falter because in some nook and cranny there exists leaven; in some area of the camp, Achan lives with his ill gotten goods; on some of the body corporate is a speck of defiling blood. Is the congregation you are in somehow defiled and will not clean itself? Has it refused to send messengers to check the tents and disposed of the sinners? Maybe it is time to separate yourself.
Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness? And what concord hath Christ with Belial? or what part hath he that believeth with an infidel? And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people. Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you, (2Co 6:14-17 – KJV)
Even in secular settings, this rule can be applied. If you are righteous, or right, then why continue with walking with someone that will defile you? How long can you live in a landfill without starting to smell like one? Without becoming a dump rat? That is why it is so important to keep ourselves separate and clean from the world, from evil, from filth. If we align ourselves with such things –people, organizations –that are wallowing in their own filth, how long can we maintain our conscience as pure and undefiled?