S Agatho's Synod was, when you think about it, quite a big one: 125 bishops. Larger, I think, than some 'Ecumenical Councils'. He was summoning it (Bede H.E. V 19) adversus eos qui ... dogmatizabant. This Synod was held against a doctrinal error that had just arisen: against those who dogmatized that there was but one Will and Working in the Lord our Saviour (i.e. Monothelites). But the Holy Father did not call his Council to find out what those 125 bishops thought, nor to discover whether they had some splendid new ideas.
Inevitably, there was an Englishman in Rome and inevitably that Englishman was S Wilfrid. This indefatigable missionary tended to find himself embroiled in rows, and his instinct on such occasions was invariably the same: go to Rome. (After all, if one got there fast enough, the Holy See only heard one side of the story!)
So S Agatho invited Wilfrid to join in his synod so as to benefit from his thinking and his erudition ... NO: not a bit of it; Wilfrid was invited to speak his Faith, in other words, to make formal confession of his orthodoxy; but not of his own merely personal Faith: that of the Province or Island from which he came. His adherence to Catholic orthodoxy was incorporated into the Acta Synodi: "Wilfrid, the God-beloved Bishop of the City of York ... was set in the seat of judgement in Synod with his 125 coepiscopi; and, in the name of (pro) the whole Northern part of Britain and Ireland, and the islands which are inhabited by the nations of the Angles and Britons, and also the Scots and the Picts, he confessed the true and Catholic Faith, et cum subscriptione sua corroboravit."
The confidence with which S Wilfrid spoke for so much of (what in Irish scholarship is now neatly called) the Atlantic Archipelago, and for the orthodoxy of thousands of Scottic monks who had never met him and, had they done so, might have had strong things to say about his Paschal Mathematics, may well take our breath away. But I want to point out what this Synod was for.
A heresy had arisen, and a previous pope (Honorius I) half a century before had actually promoted the error. Heresy is a very grave matter; but a Pope is there to condemn it. Just think of what a massive ecclesial disorder is involved if the pope himself actually favours the heresy and uses his office to spread it.
So our Holy Father Pope Agatho held a synod; and his brother bishops were there to strengthen his hand by bearing (written, formal) witness to the orthodoxy which they had, each of them, received and to which their Particular Churches bore witness. Subsequently, he called an Ecumenical Council, at which Pope Honorius, together with his fellow heresiarchs, was condemned and anathematized in the strongest possible language.
That is why, on this blog, he is known as S Agatho the Good.
The next pope, S Leo II, confirmed the Conciliar condemnations.
When will there be a Pope Agatho II? Domine, exaudi et miserere!