I think Jefferson is saying that the American People posses a spirit of resistance. That because of this spirit of resistance a Government must be transparent other wise the people will become discontented either because of truths they know about (Tea Party) or as Jefferson points out because of misconceptions (occupy wall street) In ether case he says "let them take arms" Those who do so will shed the blood of tyrants while at the same time learning the facts and justifying their cause.