John Calvin on Acts 21:18

18. All the elders were present. We may gather that out of this place which we had already in the fifteenth chapter. So often as any weighty business was to be handled, the elders were wont to come together, to the end the consultation might be more quiet without the multitude. We shall see anon, that the people were likewise admitted in their order, yet after that the elders had had their secret consultation “Interius consilium,” more private among themselves.