In horology, regulate means to be accurate and keep time. Or as I interpret it, march in time, take orders and hit your target.
No shame in that, Luv. We all have to make a living.
.
And how would you achieve that, but by constant drill?
.
More specifically, “well regulated” means to reload in time. People were still using flintlock muskets. If you were fighting as a group in close formation, you didn’t want to be pouring gunpowder while the guy next to you was firing and sending sparks flying. Everyone loads, everyone aims, everyone fires in unison. Volley fire also helped with the terrible inaccuracy of the smoothbore muskets of the era.