1 John 2:19

They went away from us, but they were not of us. For, if they had been of us, they would have abode with us; but they went away, that they might be made manifest that they were not of us.

Treasury of Scripture Knowledge

Summary

(Yea, a sword shall pierce through thy own soul also,) that the thoughts of many hearts may be revealed.

Bible References

That

1 John 2:19
They went away from us, but they were not of us. For, if they had been of us, they would have abode with us; but they went away, that they might be made manifest that they were not of us.