You know what I mean by a good man? One who is complete, finished, – whom no constraint or need can render bad. I see such a person in you, if only you go steadily on and bend to your task, and see to it that all your actions and words harmonize and correspond with each other and are stamped in the same mould [or form]. If a man's acts are out of harmony, his soul is discordant [discordant]--Seneca, Letter 34.
The underlying idea here is that we are not naturally bad, but that we are made bad by (to use anachronistic language) unsatisfied preferences. We can, thus, avoid being bad by reducing desires (need) or by removing impediments to their satisfaction (constraint). In the surface of this letter, Seneca treats the two strategies symmetrically. (In some other places he sounds more 'Stoic' by advocating the elimination of need. ) The badness consists in a lack of (what I call, recall) philosophical integrity between one's articulated ideals and actions.
Seneca here does not really confront the possibility of somebody having integrity between ideals and actions not worth having. That's because he makes two assumptions: first, and this is unstated, the unworthy ideals all presuppose desires that can't be satisfied. This is not so question-begging as it seems: most, quite ordinary forms of badness presuppose lack of moderation. But it's an open question if integrity, which is a kind of internal relation, always has (again to use anachronism) external validity.
Second, Seneca assumes the existence of the worthiness of a station and with it associated duties and tasks [id egeris]. This means that are station-relative duties are assumed to be self-justifying (as long as they do not prompt immoderate desires, etc.). Here, too, Seneca does not confront the possibility that one's station supports a status quo -- when those in charge are bad, and the empire they rule, bad too -- not worth having. As the tutor to Nero, and now former tutor, Seneca had ample time to reflect on the problem (familiar to us already from Tacitus). One sometimes wonders how many dutiful public servants recognize the problem.
This gets me to the underlying topic of the letter, which is about the nature of claiming somebody else as a student. Seneca, treats it -- and ongoing instruction -- as something violent akin to grabbing a runaway slave. Such violence may be legally sanctioned, of course. But it does not follow it is wanted.* More interestingly, perhaps, is that thereby Seneca grants that claiming somebody else as one's student is a characteristically immoderate even narcissistic action: he is explicit that for him it is the projection of an image of one's former self onto another. As if teaching another is really tantamount to redoing one's own life with the benefit of hindsight and, thereby, be rejuvenated--teaching as a means toward one's own immortality (in thought0.
The whole letter amounts to Seneca asserting [contrary, perhaps, the evidence of the Meno and Protagoras] that virtue can be taught -- and perhaps he even thinks that such assertion makes it more likely --, while simultaneously drawing attention to the fact that the very practices of teaching are implicated in a whole number of institutions and practices that seem to violate virtue (and rely on self-deception). It's an open question if the fruits of such an education can justify the means.
It's easy to imagine that when Seneca draws attention to himself, he does so as an exemplar worth emulating. But the alternative possibility -- that he draws attention to his own excessive needs as a path worth avoiding -- cannot be ruled out.
*The Latin is inieci manum, placing a hand on property. Loose and potentially violating hands are, it seems, endemic to education. It does not follow they are necessary.