In Acts 8 we learn that
When the apostles in Jerusalem heard that Samaria had accepted the word of God, they sent Peter and John to Samaria.
Presumably this sending was in order to authenticate the work going on in Samaria, to give this expansion the apostolic imprimatur. Then, in Acts 11, when the gospel is breaking new ground among the Greeks in Antioch we learn that
News of this reached the ears of the church in Jerusalem, and they sent Barnabas to Antioch.
Why send Barnabus? Not to authenticate the work but to encourage the church. For
He was a good man, full of the Holy Spirit and faith, and a great number of people were brought to the Lord.
What great vision the church in Jerusalem showed at this point. Having worked-through the reality that the Lord was indeed saving Gentiles (notice how this follows so closely the incident with Peter and Cornelius and the church's consideration of that) they felt no need to send people to check out the work but rather chose someone they knew would cheer on those involved in it.
No doubt there is much for us all to learn from their example.
