There are three ways in which someone is a soldier of Christ. First, inasmuch as he fights against sin....And this fight is against the flesh, the world, and the devil....
Second, someone is a soldier of Christ by fighting against errors....
Third, the military service of martyrs is against tyrants. And this is more laborious....And a soldier (miles) ought not to rest since he is named from the warfare to be endured (militia sustinenda).
[St. Thomas Aquinas, Commentaries on St. Paul's Epistles to Timothy, Titus, and Philemon, Baer, tr., St. Augustine's Press (South Bend, IN: 2007) pp. 110-111.]
