For any essay, it is generally useful to establish a strong thesis, which will give you a direction in which to develop a set of subsidiary arguments that will support it. Depending on the length of the essay, there could be any number of body paragraphs in which those arguments and the supporting evidence for each one would be developed. A solid introductory paragraph will lay out that thesis and mention the subsidiary points, pointing the reader to the likely path of exposition.
A character analysis of Desmond Doss could proceed chronologically or thematically. A writer could follow Doss from his initial conscientious objection to service through his heroic performance in rescuing his fellow soldiers. In that type of organization, the argument would be concerned with his personal growth. Individual paragraphs might highlight experiences that helped shape his changing views of service.
If one opts for the thematic approach, the chronological sequence is not as relevant. Rather, one would break down the central idea of conscientious objector status into the components with which Doss justified having that status. Highlighting Doss as one individual among many soldiers, the essay writer might emphasize the combat situation. Were there specific experiences that influenced Doss’s way of thinking? Did he fundamentally change his view of militarism and violence? What factors worked toward excluding or including him in the combat unit? One paragraph could focus on the other soldiers’ changing opinions as Doss proves himself by rescuing others in the height of battle.