Theme influences choices for every element in the story: plot development, characterization, and setting.
Let’s look at these elements. Here’s the shell of the plot: your father was laid off; a difficult time followed for the family; your father received additional training and obtained a different job.
Your treatment of this plot will vary according to your theme. Let’s suppose the following is your theme: “events whose consequences we can’t understand happen gratuitously to us in our lives, but we can always make the best of things.” In the elaboration of this particular theme (message), you will find it natural to set your father’s being laid off not only with his reaction at the time but also with its consequences. Because of your positive theme, you will write about the new circumstances that developed for your father and about his psychological growth (character). To develop your theme, you will show how important it was for him to “roll with the punches,” to allow himself to experience being without the identity his job and his role as family provider had furnished, and, ultimately, to exercise choices that led to new, satisfying pursuits.
So much for one plot development. Now imagine that your theme (obviously based on different insights) had been: “life deals each of us gratuitous, unwarranted dirty tricks and my father was no exception.” In this story, you would emphasize the role other people played in your father’s being laid off and how no one helped him. You would dwell on the negative elements–how the economic demands made on him by his children left him with few choices, how his insufficient education (due in turn to his parents, his ethnic group, etc.) limited his job options. You would probably undervalue the training that led to a different job and fail to acknowledge the psychological growth that he experienced as a result of training and his new job challenges.
Both of these plot developments would be based on the same facts, but the stories themselves would be very different because they are inspired by very different themes. As a writer, you must be aware that your theme (the message you seek to impart) affects the interpretation of every fact in your story. By conscious use of theme, you can make a story into your own distinct and unique account.
Good luck writing your memoir