Acts 13:2

As they (b) ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have (c) called them.

(b) While they were busy doing their office, that is, as Chrysostom expounds it, while they were preaching.

(c) The Lord is said to call, from which this word "called" comes from, which is common in the Church, when he causes that to be which was not, whether you refer it to the matter itself, or to any quality or thing about the matter: and the use of the word "call" has come about because when things begin to be, then they have some name: and furthermore this also declares God's mighty power, in that he spoke the word, and things were made.