Life is extremely complex, or at least it can seem that way. Despite all that complexity and the vastness of time and space, you still only have to decide what you are going to do right now. That is all you have control over. And how do you boil everything down - how do you get it from the complex to the comprehensible - so that you can decide how to use your time and actions now? Simply put: reason. Furthermore, the Stoics have applied their reasoning and have arrived at the conclusion of: virtue is the sole good. Therefore, if you funnel all your choices and thinking into the paradigm of "virtue is the sole good" then you will see this complex world through the lens of wisdom, justice, courage and temperance.
Extending that concept on to society and civilization; Plato perhaps saw society as full of philosophers where everyone was enlightened. It is a worthy goal. But philosophically herding humans is about as easy as herding cats. Therefore any progress you make in enlightening others ought to be celebrated as no small (mean or average) achievement.
Further in the passage, Marcus seems to be saying the alternative to enlightenment (philosophy) is slavery, which he defines as "groaning" and "going through the motions" - certainly no joy in that! Then he seems to defend men who at least preached that everyone ought to live a life philosophically, but perhaps were hypocrites ("simply strutted a dramatic role"). To which Marcus responds he certainly has the capacity to listen to reason from hypocrites, but he is absolutely not condemned to act the hypocrite - he can take the lesson without having to act like the (bad) teacher. A modern day rendition of this idea is "don't throw the baby out with the bathwater." To be clearer, however, I think the ideal scenario is to learn philosophy from sages - true Stoic sages who live what they teach.
(see also Citadel p. 271, 303-305)