Acts 13:2

As they ministered to the Lord
That is, the five prophets and teachers before mentioned; and whose ministry lay in preaching the Gospel, teaching the people the doctrines of it, and expounding prophecies, and also in prayer; to which latter the Syriac version restrains their ministry, rendering it, "as they prayed to God"; but the phrase seems to be more extensive: "and fasted"; which the Jews were much used to, and the believing ones had not yet left it off; their custom was to fast on Mondays and Thursdays: (See Gill on Luke 18:12). Whether it was on one of those days, that these men were ministering and fasting, is not certain; but this we may be sure of, it was not on the Jewish sabbath, for on that day they never fasted; very likely that this was a fast appointed and fixed among themselves, on some particular occasion; it may be on account of the famine, which was at this time, ( Acts 11:28 ) .

The Holy Ghost said;
either with an articulate voice, or by an internal impulse, upon the minds of three of the prophets:

separate me Barnabas and Saul, for the work whereunto I have
called them;
the work which the Holy Ghost had appointed, and called them to before this, was to go and preach the Gospel among the Gentiles, distinct from the Jews, of which we read in the latter part of this chapter; and now he would have them be separated from their brethren, as Aaron and his sons were from theirs, and be sent forth from hence directly, upon that work: this shows the Spirit to be a person, since speaking and commanding in an authoritative way, and calling to a work, are ascribed unto him; and that he is a divine person, and truly God, and equal with God, since calling to a sacred office is attributed to him; and a separation to it is ordered for himself, for his service, honour, and glory; he does not say separate them to the Lord, or to God, but to me.