Lactantius, Divine Institutes 6.11
Humanity must be preserved if we wish to be called human beings in the true sense. And what is preserving humanity but loving a human being because he is a human being, the same as we are? Discord and division, therefore, are not in keeping with human reason; the saying of Cicero stands true: a person who obeys nature cannot harm another person. Since harming a human being is contrary to nature, benefiting a human being must necessarily accord with nature. Anyone who fails to do so strips himself of the very name 'human,' for the duty of humanity is to come to the aid of a person in need and danger. I put this question to those who claim that being moved to pity is not the mark of the wise: if a man seized by a wild beast begs an armed man for help, do they think he ought to be rescued, or not? They are not so shameless as to deny that what humanity demands and requires must be done. Likewise, if someone is encircled by fire, crushed by a collapsing building, drowning in the sea, or swept away by a river, do they imagine it is not a man's duty to help? Let them not call themselves human if they think so — for no one can escape such dangers — but rather they will acknowledge it is the part of a human being, and of a brave man, to save one who is perishing. Since they concede that in such cases, because they threaten human life, it is humanity's duty to come to the rescue, what reason can there be for refusing to help when a man is hungry, thirsty, or cold? These conditions are equal in nature to those sudden disasters and call for the same single humanity; yet they make a distinction between them, because they measure everything not by the truth of the matter itself but by present utility. They hope that those they snatch from danger will repay them with gratitude, but they reckon that the needy — since they hold out no hope of return — will simply perish, and they consider whatever they give to such people as lost.
Latin
Conseruanda est igitur humanitas, si homines recte dici uelimus. id autem ipsum, conseruare humanitatem, quid aliut est quam diligere hominem, quia homo sit et idem quod nos sumus? -discordia igitur ac dissensio non est secundum hominis rationem uerumque illut est Ciceronis, quod ait hominem naturae oboedientem homini nocere non posse. ergo si nocere homini contra naturam est, prodesse igitur homini secundum naturam sit necesse est. quod qui non facit, hominis se appellatione despoliat, quia humanitatis officium est necessitati hominis ac periculo subuenire. quaero igitur ab iis qui flecti et misereri non putant esse sapientis, si homo ab aliqua bestia conprehensus auxilium sibi armati hominis inploret, utrumne succurrendum putent an minime. non sunt tam inpudentes, ut negent fieri oportere quod flagitat, quod exposcit humanitas. item, si aliquis circumueniatur igni, ruina opprimatur, mergatur mari, flumine rapiatur, num putent hominis esse non auxiliari. non sint ipsi homines, si putent — nemo enim potest eiusmodi periculis non esse subiectus —, immo uero et hominis et fortis uiri esse dicent seruare periturum. si ergo in eiusmodi casibus, quia periculum uitae homini adferunt, succurrere humanitatis esse concedunt, quid causae est cur, si homo esuriat sitiat algeat, succurrendum esse non putent? quae cum sint paria natura cum illis casibus fortuitis et unam eandemque humanitatem desiderent, tamen illa discernunt, quia non re ipsa uera, sed utilitate praesenti omnia metiuntur. illos enim quos periculo subripiunt sperant sibi gratiam relaturos, egentes autem quia non sperant, perire arbitrantur quidquid eiusmodi hominibus inpertiant.