Of Plymouth Plantation is significant because it chronicles facts about the establishment of the Pilgrim Church in England, the group who left for Holland and eventually the trip on the Mayflower to the New World on November 11, 1620, and the early days of colonial America. Bradford was governor of the colony for 33 years. Among many things he writes about, maybe the most famous is the first Thanksgiving.
It is also significant because it is the most lucidly reliable account of those early days in American history. One of the lessons about the Puritans in reference to their common beliefs or personalities is that they came to the New World seeking religious freedom. Bradford's work draws on many Biblical parallels. They wanted to "purify" (hence the name "Puritans") the Church of England, believing that the Protestant Reformation did not go far enough in attempting this. It also seems that their fervor for this purification in the new community in the new world eventually declined; it was said that Bradford wrote some of this text with a nostalgia, implying that their focus on their role as religious crusaders/founders of a new world gave way to expansion and maybe more focus on other aspects of life.
In Geoffrey Chaucer's The Canterbury Tales, 32 characters make the trip to Canterbury. 29 of these are mentioned in line 24 of the “General Prologue.” The narrator joins this group (making 30).
All of the above can help to develop a character. A reader will have a clearer image of the character if they are given a description of what the character looks like. We also know who they are as individuals if we know their thoughts or hear them speak. Other characters' opinions of this character can also help to develop them, because we learn who the character is through other peoples' eyes. Hope this helps.