Then all the multitude - Evidently the multitude of private Christians who were assembled on this occasion. That it does not refer to a synod of ministers and elders merely is apparent:
(1) Because the church, the brethren, are represented as having been present, and as concurring in the final opinion Acts 15:22-23; and,
(2) Because the word “multitude” τὸ πλῆθος to plēthos would not have been used in describing the collection of apostles and elders merely. Compare Luke 1:10-11, Luke 1:13; Luke 5:6; Luke 6:17; Luke 19:37; John 5:3; John 21:6; Acts 4:32; Acts 6:2; Matthew 3:7.
Gave audience - Heard, listened attentively to.
Barnabas and Paul - They were deeply interested in it, and they were qualified to give a fair statement of the facts as they had occurred.
Declaring what miracles and wonders ... - The argument here evidently is, that God had approved their work by miracles; that he gave evidence that what they did had his approbation; and that as all this was done without imposing on them the rites of the Jews, so it would follow that those were not now to be commanded.