Corteste had been appointed to Pope Paul III's Concilium delectorum cardinalium et aliorum praelatorum de emendanda Ecclesia.

[11] His mentor, Gregory Cortese, wrote to Cardinal Gasparo Contarini, expressing the hope that Chiari would be consoled by the pleasing conversation.

[13] In 1540 he published his Adhortatio ad Concordiam, already written by 1538 and dedicated to his friend Cardinal Gasparo Contarini.

[citation needed] His own edition of the Vulgate was put on the Index in 1559, and a new edition of it was authorized in 1564, but "deprived of the preface and of the prolegomenas, because those were manifestly sympathizing with the Lutheran heresy"[18][1] Following the council, on 24 January 1547, he was appointed bishop of Foligno[19] on the recommendation of Cardinals Reginald Pole, Giovanni Andrea Cortese, and Jacopo Sadoleto.

[20] At the beginning of his tenure, Bishop Isidoro summoned and presided over a diocesan synod, which met on 14 November 1547.

In 1548 he invited into his diocese the Jesuit Silvestro Landini, who helped organize confraternities for the youth to encourage frequent confession.

[25] In 1551, Bishop Chiari began to preach a series of sermons in the Cathedral on the subject of the Gospel of Saint Luke.

His view, expressed in his synods, was that preaching was a prime duty of the clergy, and at the same time he wanted his people to hear the word of God.