The way I read the Second Amendment is this:
"If the general population has to be called out and formed into a militia due to great need, we won't have time to teach them how to shoot. So everyone should be free to own and use guns."
At the end of the day it's about power. The people who are attracted to life in government always want more of it form themselves, but the framers wanted a check on that, and that check is the second amendment.
"...nor will we have resources to equip them..."