We the people . . . provide for the common defence.

Probably the best known part of the preamble, quoted by the NRA, militia groups, and anybody else who thinks that every citizen has a right to own a machine gun.
The Founding Fathers knew oratory, better than any politician today. They were also visionaries. They did not call for arms for all, nor for the establishment of an army.
They could not have predicted aircraft, bioweaponry, or hackers, but they did assume that new dangers might someday menace their new state, and they intended that the federal government should provide for it.
Note also that they intended that the defence be for everyone - a common defence. Everyone pitches in, and everyone benefits. No one is exempt from contributing.

We have managed to pervert this goal as well. The many now benefit from the few, and the few are neglected. The army lacks proper equipment - scandalous, for the richest military in the world - and it is being frittered away on a scandalous mission.
Assuming for a moment that Iraq really IS drawing all the terrorists in the world away from the United States, is it really in our best interest to have our defenders stand on a target all day for months? No wonder enlistment is down. Who wants THIS job?
Moreover, enlistments are primarily limited to the underclasses. The rich men's sons get their degrees and apprenticeships and carry guns for sport, if that.

We have no common defence. We have a career military, made up of the poor in the ranks and the incompetent in command. Now, I'm not saying that we won't survive with this system - England had just such an army in the 19th century - but it's not what the Founding Fathers wanted.
And it's not a good thing. Military recruitment is a good barometer for a nation's commitment to it's system, it's values, and it's government. Recruitment is down. What does that tell you?