Tertullian, On Idolatry 19
This chapter could also be read as settling the question of military service, which stands between dignity and power. But the question now is whether a faithful person can turn to military service, and whether military service — even the lowliest rank, or any inferior grade that does not require sacrifices or capital judgments — can be admitted to the faith. Divine and human sacrament do not go together, the sign of Christ and the sign of the devil, the camp of light and the camp of darkness: one soul cannot be owed to two masters, God and Caesar (Matt. 22; Exod. 3; Exod. 28; Matt. 3; Exod. 17; Luke 3; Matt. 8; Matt. 26). Moses carried a rod, and Aaron a buckle; John is girded with a strap; Jesus Nave led the host; the people waged war, if it pleases to play. But how will he wage war, indeed how will he even serve in peace, without a sword, since the Lord took it away? For although soldiers came to John and received a rule of observance, and even a centurion believed; afterwards the Lord disarmed every soldier in Peter. No manner of life is lawful for us if it is assigned to an unlawful act.
Latin
Posset in isto capitulo etiam de militia definitum videri, quae inter dignitatem et potestatem est. At nunc de isto quaeritur, an fidelis ad militiam converti possit, et an militia ad fidem admitti etiam caligata, vel inferior quaeque, cui non sit necessitas immolationum vel capitalium judiciorum. Non convenit sacramento divino et humano, signo Christi et signo diaboli, castris lucis et castris tenebrarum: non potest una anima duobus deberi, Deo et Caesari (Matth., XXII; Exod., III; Exod., XXVIII; Matth., III; Exod., XVII; Luc., III; Matth., VIII; Matth. XXVI). Et virgam portavit Moyses, fibulam et Aaron; cingitur loro et Joannes; agmen agit et Jesus Nave; bellavit et populus, si placet ludere. Quomodo autem bellabit, imo quomodo etiam in pace militabit, sine gladio, quem Dominus abstulit? Nam, etsi adierant milites ad Joannem, et formam observationis acceperant, si etiam centurio crediderat; omnem postea militem Dominus, in Petro exarmando, discinxit. Nullus habitus licitus est apud nos illicito actui adscriptus.