Commentary on Meditations: B10:8

Claim your entitlement to these epithets - good, decent, truthful; in mind clear, cooperative, and independent - and take care then not to swap them for other names: and if you do forfeit these titles, return to them quickly. Remember, too, that 'clarity of mind' was meant to signify for you discriminating attention to detail and vigorous thought; 'a cooperative mind' the willing acceptance of the dispensation of universal nature; 'independence of mind' the elevation of your thinking faculty above the calm or troubled affections of the flesh, above paltry fame or death or any other indifferent thing. So if you keep yourself true to these titles, not just grubbing for this acclamation from others, you will be a new man and enter a new life.

To continue the same man as you have been up to now, to be torn apart and defiled in this life you live, is just senseless self-preservation like that of half-eaten gladiators who, mauled all over and covered in blood by the wild beasts, still plead to be kept alive for the next day, when in their same state they will meet again those same claws and teeth.

Launch yourself, then, on these few claims. If you can stay within them, stay there like a man translated to some paradise, the Islands of the Blest. But if you feel yourself falling away and losing control, retire in good heart to some corner where you will regain control - or else make a complete exit from life, not in anger, but simply, freely, with integrity, making this leaving of it at least one achievement in your life.

A great help to keeping these claims to virtue fresh in your mind will be to keep your mind on the gods, remembering that what they want is not servile flattery but the development of all rational beings into their own image: they want the fig-tree to do the proper work of a fig-tree, the dog of a dog, the bee of a bee - and man the proper work of man.

"Epithet" is just a fancy way of saying "nickname."  Also, don't be confused between epithet and epitaph (see here if you need a quick lesson).  Marcus wants to be nicknamed "good" or "decent" or "truthful" or "clear in mind" or "cooperative" or "independent."  Said slightly differently, these are the things he wants to be known for - he wants these things to represent his unique character.  Could I say the same?  It is a good exercise to see if you could be nicknamed after any of these virtues.  Marcus further elaborates on 'clarity of mind' - which is nothing more than the ability to being able to pay attention to the correct details.  How many people do you know who are versed in mindless, useless, details (sports trivia, entertainment, etc)?  Now compare them with someone who remembers details of peoples' lives - people who they interact with every day (family, friends, neighbors, co-workers).  A 'cooperative mind' is one that loves its fate.  An 'independent mind' is one that is not enslaved by thinking of desires (food, sex, money, fame) all the time.

Next he likens a person who is constantly torn between the cares for indifferents and the cares of living a life of virtue, to a gladiator who has been half-eaten but wants to keep on living.  Why all the self-torture?  Better to strive for commitment to a life of virtue than to constantly be splinched between wanting to be good, but also wanting fame, sex, drugs, rock and roll.

Better to "launch yourself" - give it all you've got - to live a life of virtue.  Epictetus teaches this concept early in the Enchiridion when he says,

As you aim for such great goals, remember that you must not undertake them by acting moderately,1 but must let some things go completely and postpone others for the time being. But if you want both those great goals and also to hold public office and to be rich, then you may perhaps not get even the latter just because you aim at the former too; and you certainly will fail to get the former, which are the only things that yield freedom and happiness.

Lastly, Marcus offers some council for keeping virtues in the forefront of your mind: "keep your mind on the gods" not to solely worship or flatter them, but to reach the goal they have set for you - which is to become sages, to be made in the image of them.  The gods created fig trees to make figs.  They created dogs to act like dogs - to be loyal, protective, etc.  They created bees to be like bees - to make honey, to spread pollen.  They created humans to be like humans - to be rational and social.

(see also Citadel p. 246)