The deputy - believed - This was a proof that the doctrine was true; and that the power of God, from which nothing could be concealed, and which nothing could resist, was with these preachers.

Being astonished - Εκπλησσομενος, Being struck with astonishment, as Elymas was struck with blindness. Thus the word of God is a two-edged sword: it smites the sinner with judgment or compunction; and the sincere inquirer after truth, with conviction of its own worth and excellence.

the deputy.

Acts 13:7 Which was with the deputy of the country, Sergius Paulus, a prudent man; who called for Barnabas and Saul...

Acts 28:7 In the same quarters were possessions of the chief man of the island, whose name was Publius; who received us...

when.

Acts 19:7 And all the men were about twelve.

Matthew 27:54 Now when the centurion, and they that were with him, watching Jesus, saw the earthquake, and those things that were done...

Luke 7:16 And there came a fear on all: and they glorified God, saying, That a great prophet is risen up among us; and...

being.

Acts 6:10 And they were not able to resist the wisdom and the spirit by which he spoke.

Matthew 7:28,29 And it came to pass, when Jesus had ended these sayings, the people were astonished at his doctrine...

Luke 4:22 And all bore him witness, and wondered at the gracious words which proceeded out of his mouth. And they said, Is not this Joseph's son?

John 7:46 The officers answered, Never man spoke like this man.

2 Corinthians 10:4,5 (For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;)...

'Full of the Holy Ghost'
'And the disciples were filled with joy, and with the Holy Ghost.'--Acts xiii. 52. That joy was as strange as a garden full of flowers would be in bitter winter weather. For everything in the circumstances of these disciples tended to make them sad. They had been but just won from heathenism, and they were raw, ignorant, unfit to stand alone. Paul and Barnabas, their only guides, had been hunted out of Antioch by a mob, and it would have been no wonder if these disciples had felt as if they had been …
Alexander Maclaren—Expositions of Holy Scripture: The Acts

Ninth Day for God's Spirit on Our Mission Work
WHAT TO PRAY.--For God's Spirit on our Mission Work "The evangelisation of the world depends first of all upon a revival of prayer. Deeper than the need for men--ay, deep down at the bottom of our spiritless life, is the need for the forgotten secret of prevailing, world-wide prayer." "As they ministered to the Lord, and fasted, the Holy Ghost said, Separate Me Barnabas and Saul. Then when they had fasted and prayed, they sent them away. So they, being sent forth by the Holy Ghost, departed."--ACTS …
Andrew Murray—The Ministry of Intercession

Separated unto the Holy Ghost
"Now there were in the church that was at Antioch certain prophets and teachers; as Barnabas, and Simeon that was called Niger, and Lucius of Cyrene, and Manaen . . . and Saul. "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. "And when they had fasted and prayed, and laid their hands on them, they sent them away. So they, being sent forth by the Holy Spirit, departed unto Seleucia" (Acts 13:1-4). In the story …
Andrew Murray—Absolute Surrender