The parable of the wheat and tares is exclusive to Matt 13:24-30. It provides a challenging limitation to those who seek to impose their understanding as the basis of fellowship. Any practice of disfellowship has to encompass the whole gamut of scripture, rather than pick and choose passages which support our preferred model of operations. As brother I Collyer noted “an industrious rooting out of tares may be a mistaken zeal” , however the Lord goes further commanding such activity NOT occur.The parable follows the parable of the good sower. Perhaps the Lord is providing a deliberate counterbalance to the human tendency of those who considered themselves good ground/productive to correct or remove those who fail to meet their standards. Regardless the structure of the parable is clear enough. A field of good seed is sabotaged by an enemy sowing weeds. The IVP Background commentary suggests this was
“a kind of ryegrass known as darnel (usually translated “tares”) looked like wheat in the early stages and could only be distinguished from it when the ear appeared”
This sabotage is discovered and the servants offer to remove the offending material – ie they can distinguish it and have the power to act. However the Lord demurs. The extrication is doable but will impact surrounding good plants hence it is to be left in place until harvest at which point the weeds will be dealt with.
Some have suggested the parable has little to do with discipline within a specific community of faith. They suggest the picture is of all Christendom and disciples shouldn’t attempt to discipline those in other denominations. However this patently contradicts the circumstances the Lord outlines. The servants have both the ability to identify and the power to pluck out the false wheat. The parable is about not to exercise a power which could be utilised. This is an uncomfortable parable therefore for some, as Bro Booker notes:
By the explicit teaching of Christ, his brethren have no power nor right nor duty to exclude these “tares” from their “fellowship”. “Let both grow together until the harvest”
On the subject of the debate on origins, it is an unfortunate fact that those strongly opposed to these ideas have not implemented the Lord’s instructions. Rather through pursuing various brethren in South Australia, Victorian and Taiwan they have significantly damaged three ecclesias and many lives. Even if their judgement of EC being wrong were correct and its various adherents were indeed tares, how has this instruction of the Lord been applied?
Oh but “from such withdraw thyself” is the likely refrain (ironically a failure of bible study means this interpolation in the text is still used by the defenders of doctrine, see Metzer or most up to date translations). Perhaps a few words from John Thomas later in his life on his attitude to fellowship issues and heresy hunting:
“It is not my province to issue bulls of excommunication, but simply to shew what the truth teaches and commands. I have to do with principles, not men. If anyone say that Jesus Christ did not come in the flesh common to us all, the apostle John saith that that spirit or teacher is not of God; is the deceiver and the anti-Christ, and abides not in the doctrine of Christ; and is therefore not to be received into the house, neither to be bidden Godspeed (1 John 4:3; 2 John 7,9,10). I have nothing to add or to take from this. It is the sanctifying truth of the things concerning the ‘name of Jesus Christ’. All whom the apostles fellow-shipped, believed it; and all in the apostolic ecclesias who believed it not—and there were such—had not fellowship with the apostles, but opposed their teachings; and when they found they could not have their own way, John says, ‘They went out from us, for they—the anti-Christ—were not all of us’ (1 John 2:19). The apostles did not chase them out, but they went out of their own accord, not being able to endure sound doctrine (2 Tim. 4:3).
Rather than continue to cause damage in the community, perhaps those pursuing both individuals, and pressuring other ecclesias, could pause and consider – how are they implementing the Lord’s command? Should they rather allow space and tolerate the conscience of others?
 Keener, C. S. (1993). The IVP Bible background commentary: New Testament (Mt 13:25–27). Downers Grove, IL: InterVarsity Press.
 Carter, John “Questions and Answers” The Testimony Magazine, Vol. 39, pp. 272-4
 Booker, George (1977) “The Wheat and the Tares” Testimony Magazine Vol 47. Page 147
 Metzger, B. M., United Bible Societies. (1994). A textual commentary on the Greek New Testament, second edition a companion volume to the United Bible Societies’ Greek New Testament (4th rev. ed.) (pp. 575–576). London; New York: United Bible Societies.
 Thomas, John (1870) “Fellowship in the Truth” The Christadelphian Magazine Vol 7 page 16