But here is found a fivefold distinction among human beings.
(1) A bodily one according to sex, and this he excludes, saying 'there is no male and female', which do not differ according to mind but according to bodily sex.
(2) The second through nations, and this he excludes, 'there is neither Greek nor Jew'. For although these were believers, and those unbelievers, yet both have rational minds (Rom. 3:29, 'Is He God of the Jews only? And not of the Gentiles?')
(3) The third, according to a specific rite, for some had profession of law and others did not have that rite, yet (Rom. 10:12) 'the same Lord is Lord of all', and so forth.
(4) The other concerns language, 'barbarian, Scythian'. Scythia is towards the north, barbarism is foreignness, thus barbarians are as it were foreign. And one is simply a barbarian who is alien to human nature as such, and this is in so far as it is rational. And, therefore, barbarians are those who are not ruled by reason and law, and therefore are naturally servile. But in Christ they do not differ, because even if they do not have the civil law, yet they have the law of Christ.
(5) The other concerns condition, because some are servants, and some free; but in Christ they are all alike. (Job 3:19, 'The small and great are there', and so forth.)
Therefore these differences are not in Christ, but Christ is all and in all.
Thomas Aquinas, Super Epistolam B. Pauli ad Colossenses lectura, cap. 3, lect. 2.