Around 252 A.D. Cyprian wrote a letter to several Christians (Maximus, Urbanus, Sidonius, and Macharius) who had recently been received back into the church after they had left under persecution. They repented and confessed faith, and after time, were allowed full fellowship once again. Cyprian rejoices in this letter (“Epistle L”  in the Ante-Nicene Fathers, V.326-7) that they repented and confessed faith. Here’s part of his counsel:
“Although there seem to be tares in the Church, yet neither our faith nor our charity ought to be hindered, so that because we see that there are tares in the Church we ourselves should withdraw from the Church: we ought only to labour that we may be wheat, that when the wheat shall begin to be gathered into the Lord’s barns, we may receive fruit for our labour and work. [Cyprian then quotes 2 Tim. 2.20]”
In other words, he calls these restored brethren to “stick with” the church even though there may be tares. Calvin said it this way: “Add to this, that very many, under the pretense of zeal, are excessively displeased, when every thing is not conducted to their wish, and, because absolute purity is nowhere to be found, withdraw from the Church in a disorderly manner, or subvert and destroy it by unreasonable severity (Commentary on Matthew [13.24-43]).”
Cyprian then goes on to say, essentially, that it is not the job of humans to “do” the final separation between the wheat and the tares:
[No one] …may claim to himself what the Father has given to the Son alone, so as to think that he can take the fan for winnowing and purging the threshing floor, or can separate by human judgment all the tares from the wheat. That is a proud obstinacy and a sacrilegious presumption which a depraved madness assumes to itself. And while some are always assuming to themselves more dominion than meek justice demands, they perish from the Church; and while they insolently extol themselves, blinded by their own swelling, they lose the light of truth.”
Fascinating. Cyprian was hinting at the same things that the Reformers faced during the Reformation. With some historical/contextual clarifications, one could apply Cyprian’s latter quote to the Anabaptists of the 16th century and beyond.