Some businesses and manufactures have a position or department among their staff that is called "Quality Control." It is their job to make sure the things being produced by the company are up to certain standards. When they discover things are otherwise, they bring the matter to the attention of those in management positions, or perhaps even have the authority themselves to correct the problem.
From time to time, I have run across some self-appointed "quality control" agents in the Lord's church. These members watch everything and listen to every word spoken, sung, or prayed, and when they see or hear something they consider to be out of order, they spring into action. Often they just murmur about the "offense" among their friends, but sometimes they will rebuke the "offender" and demand he make a public correction. While their methods are almost always harsh, they justify their action and attitude with the worn-out slogan, "I am just trying to keep the church pure." An unfortunate trait of these "quality control" agents is they are unwilling to do anything but observe and criticize. It is as if their only contribution to the local church is to watch and criticize. They do not dare put themselves in a position to have their efforts criticized. They do not lead the church in its worship, take their turn teaching a Bible class, extending an invitation, or preaching. They do not visit the sick or shut-ins (but somehow know when the elders or preacher fails to do so). They don't do anything but complain.
While every member should have a genuine concern for the purity of the local church, and should be willing to meekly approach those who have misspoken while leading us in our worship or Bible study, there is no room in the local church for a self-appointed "quality control" agent. We have work to do (Eph. 4:16). Let's all get busy.