Agobard, archbishop of Lyon from 816, writes against the Adoptionist heresy—i.e., that Jesus was not the son of God by nature but by adoption—of Felix of Urge, who had been confined at Lyon from 800 to 818, and against the Jews.

In 820, he “proves” that Jews are born slaves and accursed.

He forcibly converts Jewish children, offering them and their parents no choice in the matter; the “choice” of expulsion is, for the first time in Carolingian domains, not an option.

Agobard's anti-Jewish essays, a few of which survive, are systematically aimed at humiliating and eradicating Francia’s Jewish community, referring to Jews as "sons of darkness".

In his writings against popular superstitions, he denounces the trial by ordeal of fire and water, the belief in witchcraft, and the ascription of tempests to magic, maintains the Carolingian opposition to image-worship, but carries his logic farther and opposes the adoration of the saints.

In his purely theological works, Agobard is strictly orthodox, denying the verbal inspiration of Scripture.

As many clerics, Agobard is a proponent of the unity of the Frankish Empire.

Hence, he opposes the Empress Judith's initiatives on behalf of her son Charles the Bald and supports the rebellion of Charles' half-brothers Lothair and Pepin against their father, Emperor Louis “the Pious”, the son and successor of Charlemagne and the fourth monarch of the Carolingian dynasty.