Assuming it isn't all more Obi-Wan point of view style fibs, the Jedi Knights were guardians of peace and justice for a thousand generations.
Consider how ineffectual the UN peace keeping missions are and multiply that by the billions of worlds in the Republic. Are these knights some sort of inquisitors as well? They don't just keep the peace they keep justice too and they have the power to enter the minds of some people.
To be effective as guardians of peace there has to be millions of Jedi Knights all over the place and working hard and being quite openly active for their memory to be revered and despised almost two decades after being systematically rounded up and destroyed.
A thousand generations (assuming he means human generations) is a long time.
They can't all just be hermits hiding up a hill in the middle of nowhere.
However from a certain point of view anyone can guard a whole galaxy :
