Warfare is twofold: one is spiritual, and the other is carnal. II Cor 10:4: For the weapons of our warfare are not carnal, but mighty to God unto the pulling down of fortifications, destroying counsels, etc. In a good warfare two things are required on the part of the soldier: that he do nothing contrary to military discipline and that he not faint in idleness.... Likewise, on the part of the warfare two things are required: that it fight off those contrary to the republic and that it subject those who need to be subject. Thus also spiritual warfare is ordered to destroying everyone who extols himself and to subjecting every intelligence unto obedience to Christ, as it is said in II Cor. 10....
He says, therefore, that thou war in them, etc., as if to say: You can fight a good war first through the good faith which you have...And through a good conscience, since a man easily departs from waht harms him; hence, remorse of conscience is as a certain stimulus which stings a man with a bad conscience, and so he quickly falls away from sin through a good conscience and right faith.
[Thomas Aquinas, Commentaries on St. Paul's Epistles to Timothy, Titus, and Philemon, Baer, tr. St. Augustine's Press (South Bend, IN: 2007), p. 20.]
