Chapter — Marc, Institutiones Morales
Chapter III: On Sins Opposed to Faith
St. Thomas, 2.2, q. 10-12; St. Alphonsus, II, 17; ed. G., I, p. 309; Lugo, disp. XVIII seqq.; Aertnys, l. II, n. 9; Lehmkuhl, 1, 410; Tanquerey, II, n. 655; Gury-Ferreres, I, n. 205 seq.; Gopfert, 1, § 47.
- To the virtue of faith is opposed, by EXCESS, rash credulity, by which, from levity of heart, things are believed as belonging to the Christian faith and religion, when they are not such; as, for example, if someone lightly believed and handed on to others private revelations very suspect and doubtful. - Hence St. John warns (1 Ep. 4:1): Dearly beloved, do not believe every spirit, but test the spirits whether they are of God. But, the danger of losing true faith being excluded, the aforesaid credulity will be a venial sin, or none.
By DEFECT, to the virtue of faith are opposed: 1. Sins of omission, namely negligence in learning truths of faith necessary to know; and omission of acts which the affirmative precept of faith prescribes (cf. n. 428). Yet by these sins the infused habit of faith is not lost. 2. Sins of commission, namely denial of faith, whether external or internal, which the negative precept forbids (cf. n. 429). But since internal denial of faith is made especially through infidelity, heresy, and apostasy, and since the dangers of these sins also are prescribed to be avoided, we shall treat here: a) of infidelity; b) of heresy and apostasy from faith; c) of avoiding dangers of losing faith.