They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
All Commentaries on 1 John 2:19 Go To 1 John 2
Cyprian of Carthage
AD 258
Has once learned, never departs from Him at all, and that those are the Church who remain in the house of God; but that, on the other hand, they are not the plantation planted by God the Father, whom we see not to be established with the stability of wheat, but blown about like chaff by the breath of the enemy scattering them, of whom John also in his epistle says, "They went out from us, but they were not of us; for if they had been of us, no doubt they would have continued with us.".
The Apostle John execrates and severely assails these, when he says, "They went forth from us, but they were not of us; for if they had been of us, surely they would have continued with us."
