We must now consider disobedience, under which head there are two points of inquiry:
(1) Whether it is a mortal sin?
(2) Whether it is the most grievous of sins? _______________________
FIRST ARTICLE [II-II, Q. 105, Art. 2]
Whether Disobedience Is a Mortal Sin?
Objection 1: It seems that disobedience is not a mortal sin. For every sin is a disobedience, as appears from Ambrose's definition given above (Q. 104, A. 2, Obj. 1). Therefore if disobedience were a mortal sin, every sin would be mortal.
Obj. 2: Further, Gregory says (Moral. xxxi) that disobedience is born of vainglory. But vainglory is not a mortal sin. Neither therefore is disobedience.
Obj. 3: Further, a person is said to be disobedient when he does not fulfil a superior's command. But superiors often issue so many commands that it is seldom, if ever, possible to fulfil them. Therefore if disobedience were a mortal sin, it would follow that man cannot avoid mortal sin, which is absurd. Wherefore disobedience is not a mortal sin.
On the contrary, The sin of disobedience to parents is reckoned (Rom. 1:30; 2 Tim. 3:2) among other mortal sins.
I answer that, As stated above (Q. 24, A. 12; I-II, Q. 72, A. 5; I-II, Q. 88, A. 1), a mortal sin is one that is contrary to charity which is the cause of spiritual life. Now by charity we love God and our neighbor. The charity of God requires that we obey His commandments, as stated above (Q. 24, A. 12). Therefore to be disobedient to the commandments of God is a mortal sin, because it is contrary to the love of God.