This is an interesting pair of choices. Bradford's Of Plymouth Plantation is, at its core, a journal. To that extent, it's an attempt to document the literal movements and insights of these colonists, of which he is a part. That makes the case for history first. Given that, he also records the spiritual journey--its successes and failures--of these colonists. What's intriguing about the journal is that, while it does reflect his personal journey, it's clearly written for others to read. When they do, the result is spiritual inspiration.
Here's a specific reason for the dilemma represented by this writing--history or spiritual inspiration. Chapter one is called "History of Plymouth Plantation." There's the case for history. What follows is several paragraphs about the spiritual history of England, including references to both Foxe's Book of Martyrs and Queen Mary. There's a case for both purposes, though the content is clearly more spiritual than historical. Then Bradford says this:
But that I may come more near my intendmente; ...many became inlightened by the word of God, and had their ignorante and sins discovered unto them, and begane by his grace to reforme their lives, and make consciente of their wayes, the worke of God was no sooner manifest in them, but presently they were both scoffed and scorned by the prophane multitude, and the ministers urged with the yoak of subscription, or else must be silenced; and the poore people were so vexed with apparators, and pursuants,and the comissarie courts, as truly their affIiction was not smale; which, notwithstanding, they bore sundrie years with much patience, till they were occasioned (by the continuance and encrease of these troubls, and other means which the Lord raised up in those days) to see further into things by the light of the word of God.
His first phrase, "But that I may come more near my intendmente [intention]," is a reminder that his point is to tell the story--the history--of these particular pilgrims. In order to do so, as seen in the passage above, he must write about both their physical journey (their trials, tribulations, and travels) and their spiritual journey (their transforming faith and God's continual provision). Because these were a people who were moved by God's grace and then moved, literally, by God's provision, their story is inextricably linked to God.
In short, then, Bradford's writing is a history of people totally committed to God; in telling their complete history (both physical and spiritual), his writing also serves as spiritual inspiration.