I follow PragerU on Instagram. Often 1 of their guys will go out in public & many times to University campuses do open mic Q & A on basic history questions. Questions like, "What is the 4th of July?' or "Who was the 1st President of the USA?" And especially when ask young people, they have NO Clue. Some do but many do NOT.
Maybe Trump was challenging American's to remember the history of why we are as a nation, are a nation, why we have remained strong against those who would seek to defeat freedom and how we need a new generation to step up to keep us free through service in the military. Of course he spoke to serving others wherever we live and being an influence for good as American's.
I think also that at a time when other nations & those who have declared themselves to be our enemies may think we are weakening in our resolve and defense of freedom, that Trump wanted to put it in their face that we are strong militarily and we have the capacity to defend freedom if we need to do so.
Good for him. Good for the nation. Good for old fashioned American patriotism to be on display for the nation as a whole and the younger generation, which has had little of it in recent years.