Certain passages in the Old Testament sanctioned forms of slavery.[1] The New Testament taught slaves to obey their masters,[2] but this was not an endorsement of slavery, but an appeal to Christian slaves to honor their masters and accept their suffering for Christ's sake,[3] in imitation of him.[4] In proclaiming baptism for all, the Church recognized that all men were fundamentally equal.[5] After the legalisation of Christianity under the Roman Empire, there was a growing sentiment that many kinds of slavery were not compatible with Christian conceptions of charity and justice; some argued against all forms of slavery while others, including the influential Thomas Aquinas, argued the case for penal slavery subject to certain restrictions. The Christian west did succeed in almost entirely enforcing that a free Christian could not be enslaved, for example when a captive in war, but this itself was subject to continual improvement and was not consistently applied throughout history. The Middle Ages also witnessed the emergence of orders of monks such as the Mercedarians who were founded for the purpose of ransoming Christian slaves.