In 1666, at the age of just 31, Spener was appointed Senior Pastor of the Predigerministerium (council of pastors) in the Free Imperial City of Frankfurt am Main. For the next twenty years, he held the highest church office in the city.
Spener’s letters from his time in Frankfurt cover those years that were decisive and constitutive for later Pietism. The first collegium pietatis gathered in 1670 in Frankfurt under Spener’s direction. Here, in 1675, he presented his thoughts about the necessity for a ”God-pleasing improvement of the Protestant church” in his Pia Desideria. Here, too, the new and still fragile network among the early Pietists showed tangible weaknesses when the so-called “Saalhof Pietists” separated from Spener’s congregation in 1682.
Yet, along with the great milestones of the years of Pietism’s origins, Spener’s development into one of the most significant clergymen of his time also becomes evident. The early, mostly Latin letters are directed to a relatively few addressees and are rather classical scholarly letters. Then, Spener’s network of correspondence expanded from year to year until, by 1686, he wrote increasingly in German to addressees from the most diverse social strata.
The edition of the Frankfurt period comprises as a whole ca. 1350 letters.