They were not of us — When they went; their hearts were before departed from God, otherwise, they would have continued with us: but they went out, that they might be made manifest — That is, this was made manifest by their going out.
Related Commentaries of 1 John 2:19
1 John 2:19
19 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.