As they ministered to the Lord (leitourgountōn autōn toi kuriōi). Genitive absolute of leitourgeō, old verb, used of the Attic orators who served the state at their own cost leōs or laos, people, and ergon, work or service). Common in the lxx of the priests who served in the tabernacle (Exo 28:31, Exo 28:39) like leitourgia (Luk 1:23) which see. So in Heb 10:11. In Rom 15:27 of aiding others in poverty. Here of worship (prayer, exhortation, fasting). The word liturgy grows out of this use.
And fasted (kai nēsteuontōn). Genitive absolute also. Christian Jews were keeping up the Jewish fast (Luk 18:12). Note fasting also in the choice of elders for the Mission Churches (Act 14:23). Fasting was not obligatory on the Christians, but they were facing a great emergency in giving the gospel to the Gentile world.
Separate me (aphorisate dē moi). First aorist active imperative of aphorizō, old verb to mark off boundaries or horizon, used by Paul of his call (Rom 1:1; Gal 1:15). The Greek has dē, a shortened form of ēdē and like Latin jam and German doch, now therefore. It ought to be preserved in the translation. Cf. Luk 2:15; Act 15:36; 1Co 6:20. Moi is the ethical dative. As in Act 13:1Barnabas is named before Saul. Both had been called to ministry long ago, but now this call is to the special campaign among the Gentiles. Both had been active and useful in such work.
Whereunto (ho). Here eis has to be repeated from eis to ergon just before, “for which” as Jesus sent the twelve and the seventy in pairs, so here. Paul nearly always had one or more companions.