It seemed good, etc. The formula is remarkable. It implies the consciousness on the part of the council that they had "the mind of the Spirit;" but how this mind of the Spirit was communicated we are not expressly told.
There may have been some "revelation," similar to that recorded in Acts 13:2; Acts 10:19; Galatians 2:1, etc. It is, however, generally understood as resting upon Christ's promise to be with his Church always.
Hefele quotes Cyprian as writing to Pope Cornelius in the name of the Council of A.D. 252: "Placuit nobis, Sancto Spiritu suggerente;" and the Synod of Aries as saying, "Placuit, praesenti Spiritu Sancto."
And this is the general language of the synods. Constantine claimed for the decrees of the three hundred bishops at Nicaea the same authority as if they had been "solius Filii Dei sententia." But, as Bishop Wordsworth on Acts 15:28 wisely says, "It cannot be held that councils of the Church now are entitled to adopt the words of the text in the framing of canons."