How that it is an unlawful thing (hōs athemiton estin). The conjunction hōs is sometimes equivalent to hoti (that). The old form of athemitos was athemistos from themisto (themizō, themis, law custom) and a privative. In the N.T. only here and 1Pe 4:3 (Peter both times). But there is no O.T. regulation forbidding such social contact with Gentiles, though the rabbis had added it and had made it binding by custom. There is nothing more binding on the average person than social custom. On coming from the market an orthodox Jew was expected to immerse to avoid defilement (Edersheim, Jewish Social Life, pp. 26-28; Taylor’s Sayings of the Jewish Fathers, pp. 15, 26, 137, second edition). See also Act 11:3; Gal 2:12. It is that middle wall of partition between Jew and Gentile (Eph 2:14) which Jesus broke down.
One of another nation (allophulōi). Dative case of an old adjective, but only here in the N.T. (allos, another, phulon, race). Both Juvenal (Sat. XIV. 104, 105) and Tacitus (History, Gal 2:5) speak of the Jewish exclusiveness and separation from Gentiles.
And yet unto (kamoi). Dative of the emphatic pronoun (note position of prominence) with kai (crasis) meaning here “and yet” or adversative “but” as often with kai which is by no means always merely the connective “and” (Robertson, Grammar, pp. 1182f.). Now Peter takes back both the adjectives used in his protest to the Lord (Act 10:14) “common and unclean.” It is a long journey that Peter has made. He here refers to “no one” (mēdena), not to “things,” but that is great progress.