Although the movie version of The Last of the Mohicans was entertaining and well filmed with an insistent, haunting tone set by the Gaelic music, it bears only a peripheral relationship to the Cooper novel and tends to shade our view of the main characters.
The novel is a stark revelation of the nature of the various individuals within the setting of the frontier. Hawkeye (Le Longue Carabine) is an example of a character whose lineage and personal history is little known and little revealed by Cooper and appears, at least in this novel, full blown and full grown with little narative devoted to development of his character.. (Natty Bumppo, however is the hero of several previous novels within Cooper's Leatherstocking Talesfrom which some of his character can be discerned.
Throughout, an underlying theme is quite apparent... that of what we, today, would see as overt racisim. Cooper was a man of his times and portrayed mores and views common to the time. Bumppo sees virtue in being an "unmixed white man", although largely illterate (see his exchange with the hapless David Gamut). Somewhat disconcerting, he also sees himself as a native "atheist" when considering the Christianity promoted by Gamut and others. Although he has only a passing knowledge of the Bible, he sees himself as superior in every respect (save, possibly, the equally pure-bred Uncas) and independent of the European version of "religion" to which his repeated phrase largely refers.
As you've noted, the phrase is recurring and has been the center of many essays on the novel and Cooper's ultimate purpose...