Albert Barnes Commentary Acts 13:2

"And as they ministered to the Lord, and fasted, the Holy Spirit said, Separate me Barnabas and Saul for the work whereunto I have called them." — Acts 13:2 (ASV)

As they ministered to the Lord. It is probable that this took place on some day set apart for fasting and prayer. The expression "ministered to the Lord" means that they were engaged in prayer to the Lord, or that they were engaged in divine service. The Syriac renders the passage this way.

The Holy Ghost said. Evidently by direct revelation.

Separate me. Set apart to me, or for my service. It does not mean to ordain, but simply to designate, or appoint to this specific work.

For the work whereunto I have called them. This was not the apostolic office, for Saul was called to that by the express revelation of Jesus Christ (Galatians 1:12), and Barnabas was not an apostle. The "work" to which they were now set apart was that of preaching the gospel in the regions around Antioch. It was not any permanent office in the church, but was a temporary designation to a missionary enterprise in extending the gospel, especially through Asia Minor and the adjacent regions. Accordingly, when, in the fulfillment of this appointment, they had travelled through Seleucia, Cyprus, Paphos, Pamphylia, Pisidia, etc., they returned to Antioch, having fulfilled the work to which they were separated .

Whereunto I have called them.

This proves that they received their commission to this work directly from God the Holy Spirit. It is possible that Paul and Barnabas had been influenced by the Spirit to engage in this work, but they were to be sent forth by the concurrence and designation of the church.