Again, the commandments of God contain the precept of obedience to superiors. Wherefore also disobedience to the commands of a superior is a mortal sin, as being contrary to the love of God, according to Rom. 13:2, "He that resisteth the power, resisteth the ordinance of God." It is also contrary to the love of our neighbor, as it withdraws from the superior who is our neighbor the obedience that is his due.
Reply Obj. 1: The definition given by Ambrose refers to mortal sin, which has the character of perfect sin. Venial sin is not disobedience, because it is not contrary to a precept, but beside it. Nor again is every mortal sin disobedience, properly and essentially, but only when one contemns a precept, since moral acts take their species from the end. And when a thing is done contrary to a precept, not in contempt of the precept, but with some other purpose, it is not a sin of disobedience except materially, and belongs formally to another species of sin.
Reply Obj. 2: Vainglory desires display of excellence. And since it seems to point to a certain excellence that one be not subject to another's command, it follows that disobedience arises from vainglory. But there is nothing to hinder mortal sin from arising out of venial sin, since venial sin is a disposition to mortal.
Reply Obj. 3: No one is bound to do the impossible: wherefore if a superior makes a heap of precepts and lays them upon his subjects, so that they are unable to fulfil them, they are excused from sin. Wherefore superiors should refrain from making a multitude of precepts. _______________________
SECOND ARTICLE [II-II, Q. 105, Art. 2]
Whether Disobedience Is the Most Grievous of Sins?
Objection 1: It seems that disobedience is the most grievous of sins. For it is written (1 Kings 15:23): "It is like the sin of witchcraft to rebel, and like the crime of idolatry to refuse to obey." But idolatry is the most grievous of sins, as stated above (Q. 94, A. 3). Therefore disobedience is the most grievous of sins.
Obj. 2: Further, the sin against the Holy Ghost is one that removes the obstacles of sin, as stated above (Q. 14, A. 2). Now disobedience makes a man contemn a precept which, more than anything, prevents a man from sinning. Therefore disobedience is a sin against the Holy Ghost, and consequently is the most grievous of sins.
Obj. 3: Further, the Apostle says (Rom. 5:19) that "by the disobedience of one man, many were made sinners." Now the cause is seemingly greater than its effect. Therefore disobedience seems to be a more grievous sin than the others that are caused thereby.
On the contrary, Contempt of the commander is a more grievous sin than contempt of his command. Now some sins are against the very person of the commander, such as blasphemy and murder. Therefore disobedience is not the most grievous of sins.