Lactantius wasn’t very familiar with scripture evidently.
2 Corinthians 6:16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people.
“Heretics bring sentence upon themselves since they by their own choice withdraw from the Church, a withdrawal which, since they are aware of it, constitutes damnation. Between heresy and schism there is this difference: that heresy involves perverse doctrine, while schism separates one from the Church on account of disagreement with the bishop. Nevertheless, there is no schism which does not trump up a heresy to justify its departure from the Church” (Commentary on Titus 3:10–11 [A.D. 386]). ~ St. Jerome