Bruchko: The Astonishing True Story of a 19-Year-Old American, His Capture by the Motilone Indians and His Adventures in Christianizing the Stone Age Tribe

As a book rooted in evangelical Christianity, Bruchko regularly references the Gospel, which denotes the teachings of Jesus Christ, particularly his message of salvation and redemption. This encompasses the central beliefs of Christianity, including the death, burial, and resurrection of Jesus Christ, and the promise of eternal life through faith in him. The word "gospel" translates to meaning "good news," and evangelical Christians believe it to be just that; by telling Indigenous populations about it, they are sharing the "good news" of Christianity.

The Lutheran Church, a significant branch of Protestant Christianity, originates from the teachings of the German priest and theologian Martin Luther during the 16th century. Central to its doctrine is the belief in justification by grace through faith alone, along with a rejection of papal authority in favor of the Bible's supremacy in matters of faith. Olson was born into the Lutheran Church, and his father was a devout Lutheran. However, Olson eventually departs from the church, viewing it as inadequate in fully embodying the essence of faith.

A missionary is an emissary representing a particular religious tradition (in Bruchko, it is evangelical Christianity), tasked with bringing the message of their religion to a group that is unfamiliar with it. Missionaries often try to reach uncontacted, or rarely contacted, groups of people and introduce modern antibiotics, education, and religion to them in an attempt to better their lives. Normally, missionaries are affiliated with mission agencies, organizations that coordinate missionary work through training, logistical help, and financial support. Many organize fundraising efforts in their local areas to support missionary projects. Olson is unique in pursuing “freelance” missionary work after a mission agency turned him down.