(19) They went out from us, but they were not of us; for if they had been of us, (o) they would [no doubt] have continued with us: (20) but [they went out], that they might be made manifest that they were not all of us.
(19) A digression against certain offences and stumbling blocks at which that young age especially might stumble and be shaken, Therefore that they should not be terrified with the falling back of certain, first he makes plain to men that although those who fall from God and his religion had a place in the Church, yet they were never of the Church: because the Church is the company of the elect, who cannot perish, and therefore cannot fall from Christ.
(o) So then the elect can never fall from grace.
(20) Secondly, he shows that these things happen to the benefit of the Church, that hypocrites may be plainly known.