A brilliant man once said the following:
A few good things to possibly include in a motivational statement:
-why do you want to become an officer of the navy
-what makes you qualified to meet the demanding role of a naval officer
-any leadership experience you've had and how you can contribute it to the navy
-how being an officer in the navy will influence your life and help you in the future
-if you want to be a pilot, don't just focus on the "i want to fly" aspect, spend a considerable portion (if not most) of your essay to solely talk about your aspirations to just become a naval officer.
A few things to not include in a motivational statement.
-your desires to get a sex change
-how your only interest is to bomb people in an F-18
-ranting and raving about how you only want to fly fighter planes because you saw top gun and wanted to be like maverick, etc----
All of this is just my opinion. Other people on this forum probably have their own ideas about what should be included or not, but these were the first that came to my mind. Hope it helps!