Please summarize (also include the main theme) of the Introduction of the book The Jesuit Relations: Natives and Missionaries in Seventeenth-Century North America by Allan Greer.

The Introduction of the book provides background information on the Jesuits in Canada and on Iroquois and Algonquins whom they tried to convert. The Relations were annual reports that the missionaries sent home to Paris from 1632 to 1673 about their success in converting the Native Americans they encountered. The main idea of the Introduction is that even though the Jesuits intended to convert the Native Americans, they lived with and among them for years and came to know them well. As Greer writes about the Jesuits, "they came to know native peoples as few other Europeans did" (page 1). Also, as the Jesuits were skilled and prolific writers, they left what Greer calls "the most important set of documentary materials on the seventeenth-century encounter of Europeans and native North Americans" (page 1). In other words, the Relations provide unparalleled information about the Native American tribes in New France and their interaction with Europeans.
Greer provides background information on the Jesuits, who he describes as both mystical and "ruthlessly rational in pursuit of their goals" (page 2). Their missionary drive led them to experience many cultures, including in Asia and Latin America. They were patient students of the languages and cultures they encountered. 
The author also provides background on the Algonquians (which the author refers to "Algonquinians") and Iroquois (or "Iroquoians" as Greer calls them, who were beginning to experience cultural change in the 1620s and onward. The Jesuits directed most of their missionary activity towards these two groups. The writings in Jesuit Relations describe the profound changes that these Native American groups were experiencing upon contact with Europeans.
The author also discusses the Canadian missions that were established starting in 1632 (though there were earlier, unsuccessful missions). Though they had rivals, the Jesuits were the primary religious group in New France at the time. The missions largely struggled until the 1640s, when some adults began to covert to Catholicism, often because of disease, attacks by hostile Native Americans, and growing economic dependency on Europeans.
Finally, Greer provides background on the Relations. The missionaries wrote the Relations for religious adherents back home, as well as for interested readers. The writings in the Relations combine travel narratives, ethnographic descriptions, and chronicles of firsthand experiences among the tribes. There is very little information about the readership of the Relations back in France, but historians know that religious figures and audiences read them avidly.