Soter is known for declaring that marriage was valid only as a sacrament blessed by a priest and also for formally inaugurating Easter as an annual festival in Rome.

"[5] The Montanist movement, which originated in Asia Minor, made its way to Rome and Gaul in the second half of the 2nd century, during the reign of Eleuterus.

During the violent persecution at Lyon, in 177, local confessors wrote from their prison concerning the new movement to the Asiatic and Phrygian communities as well as to Pope Eleuterus.

It appears from statements of Eusebius concerning these letters that the Christians of Lyon, though opposed to the Montanist movement, advocated patience and pleaded for the preservation of ecclesiastical unity.

[7] The Praedestinatorum Haeresis (once attributed to Augustine of Hippo, but now considered to be the work of an unknown author) states that "Holy Soter, Pope of the City, wrote against them a book, as did the master, Apollonius of Ephesus.