His grandfather, Baron Dettmar Basse, born in Iserlohn in the Ruhr Valley in what was then the Grand Duchy of Hesse and later became Germany, spent a decade in Paris as a diplomat and merchant before fleeing the Napoleonic Wars and emigrating to Philadelphia and then Pittsburgh in 1801.

Drawn by the prospect of religious freedom and economic opportunity, the widower Baron bought 10,000 acres along Connoquenessing Creek in Butler County, Pennsylvania, began building a stone, brick, and wood framed castle, and founded (with Christian Buhl) a new town complete with sawmill, brickyard, and an iron furnace.

[1][2] He also traveled and sent glowing letters back to Germany, persuading his daughter and her new husband (a French Huguenot who fled after repeal of the Edict of Nantes) to emigrate in 1807 from Frankfurt.

[3] The Baron experienced financial reverses at the war's end, and eventually sold Bassenheim to Daniel Beltzhoover and headed back to Germany in 1818, dying in Mannheim in 1836.

In addition to his studies, Passavant taught Sunday school and sold subscriptions to the Lutherische Kirchenzeitung (published in Philadelphia beginning in 1838), as well as an English-language Reform magazine, the Observer.

[8] After taking a year off from his studies due to the unexpected death of his eldest brother, Detmar, in Pittsburgh, Passavant entered the Gettysburg Seminary under Samuel Schmucker to prepare for a pastoral career.

[10] There, Passavant continued his Sunday School work, and also canvassed for the Pennsylvania Bible Society, sought funds for the Protestant mission in Cincinnati, Ohio, and attended revival meetings that his father considered too Methodistic.

[17] While in Germany, Passavant met Pastor Theodore Fliedner who had opened a hospital and training school for deaconesses in Kaiserswerth, near Düsseldorf and the Basse family's traditional estates.

[18][19] Especially after his Continental tour, Passavant became known for addressing important social issues, including slavery before the American Civil War (in which he served as a chaplain) and the needs of German and Scandinavian immigrants and freed blacks.

After his father's death in 1858, Passavant accepted a position as pastor of Christ Lutheran Church in Baden, Pennsylvania, along the Ohio River, where he served for 21 years (until 1879), while also traveling, publishing, and corresponding both within the United States and abroad.