Dating from 1836, he had supported the Pietist revivalist movement led by Savonian farmer and lay preacher Paavo Ruotsalainen.

The rationalist diocesan chapter begun to dislike Hedberg's activity because of his Pietism and he was transferred first to Paimio in 1838 and again in 1840 as prison chaplain in Oulu.

He started a short-lived and somewhat polemical publication, Evangelisten, in 1849, but its publishing was taken over by Anders Wiberg in 1851 and Per Palmqvist served as editor until it was discontinued at the end of the year.

Gradually, Hedberg discovered Lutheranism without any "order of salvation" from Martin Luther's postil and abandoned Pietism including the books of Arndt and Spener among others, which had formerly been his spiritual authorities.

Hedberg now began a controversy against Pietism, using the works of Johann Gerhard, Andreas Gottlob Rudelbach, Wilhelm Löhe, Gottfried Thomasius, Gottlieb Christoph Adolf von Harless and Catenhusen.

Also in Sweden he had many readers associated with Carl Olof Rosenius, including Baptist pioneer brothers Per Palmqvist and Gustaf Palmquist.