A.T. Robertson Commentary Acts 15:6

"And the apostles and the elders were gathered together to consider of this matter." — Acts 15:6 (ASV)

Were gathered together (συνηχθησαν). First aorist (effective) passive indicative. The church is not named here as in verse 4, but we know from verses 12-22 that the whole church came together this time also along with the apostles and elders.

Of this matter (περ του λογου τουτου). Same idiom in 8:21; 19:38. They realized the importance of the issue.