The Stoics made a claim far stronger than a recommendation to behave well: virtue is the only genuine good, vice the only genuine evil, and everything else - health, wealth, reputation, even life - is neither. On that view a good person being tortured is doing better than a corrupt one on a throne, because the only thing that can damage a life is the character of the person living it.
That is the argument these passages are making. Seneca puts it as plainly as anyone: it is not a good thing to live, but to live well.
50 passages
"Let our line of conduct, if it would not depart from its model, preserve this direction, and let us not act honourably because we are hired to do so."
"We declare that Augustus was a good emperor, and that he was well worthy to bear his parent's name, for no other reason than because he did not even show cruelty in avenging personal insults, which most princes feel more keenly than actual injuries; because he smiled at scandalous jests against himself, because it was evident that he himself suffered when he punished others, because he was so far from putting to death even those whom he had convicted of intriguing with his daughter, that when they were banished he gave them passports to enable them to travel more safely."
"1 Whoever thinks any other thing to be good except those things which depend on the will, let him envy, let him desire, let him flatter, let him be perturbed; whoever considers anything else to be evil, let him grieve, let him lament, let him weep, let him be unhappy."
"But that which we speak of as desirable for itself is such, that although it may possess some attendant advantages, yet it would be desirable even if stripped of all these."
"Besides this you inquire where and how you ought to bestow a benefit, which would not need to be done if the bestowal of a benefit was desirable in itself: because in whatever place and whatever manner it might be bestowed, it still would be a benefit." We seek to do honourable acts, solely because they are honourable; yet even though we need think of nothing else, we consider to whom we shall do them, and when, and how; for in these points the act has its being."
"What can be more base than for a man to consider what it costs him to be a good man, when virtue neither allures by gain nor deters by loss, and is so far from bribing any one with hopes and promises, that on the other hand she bids them spend money upon herself, and often consists in voluntary gifts?"
"They concern good and evil, how nothing is good for man which does not make him just, sober, brave and free; nothing evil which does not produce effects the opposite of these."
"But see if he has the advantage over you in being faithful, in being modest: for you will not find it to be so; but wherein you are superior, there you will find that you have the advantage."
"These two persons, who did not wish to be restored to their homes at the cost of a public disaster, but preferred that two should suffer unjustly than that all should suffer alike, are thought to have acted like good citizens; and in like manner it does not accord with the character of a grateful man, to wish that his benefactor may fall into troubles which he may dispel; because, even though he may mean well to him, yet he wishes him evil."
"But I, because I have seen that the nature of good is the right, and of ill the wrong, and that the nature of the man himself who does wrong is akin to my own (not of the same blood and seed, but partaking with me in mind, that is in a portion of divinity), I can neither be harmed by any of them, for no man will involve me in wrong, nor can I be angry with my kinsman or hate him; for we have come into the world to work together, like feet, like hands, like eyelids, like the rows of upper and lower teeth."
"Only the wise man possesses everything without having to struggle to retain it; he alone does not need to send ambassadors across the seas, measure out camps upon hostile shores, place garrisons in commanding forts, or manoeuvre legions and squadrons of cavalry."
""How," do you ask, "can you make them your own?" "By giving them away." Do, then, what is best for your own interests, and gain a sure enjoyment of them, which cannot be taken from you, making them at once more certainly yours, and more honorable to you."
"Regret is blame of oneself for having let something useful go by; but the good must be something useful and worth the attention of a really good man."
"To your own, to make it a righteous mind; to that of the Whole, to remind yourself what it is of which you are a part; to this man's, that you may observe whether it is ignorance or design, and may reflect at the same time that his self is of one kind with your own."
"If you complete the present work, following the rule of right, earnestly, with all your might, with kindness, and admit no side issue, but preserve your own divinity pure and erect, as if you have this moment to restore it; if you make this secure, expecting nothing and avoiding nothing, but content with present action in accord with Nature and with heroic truth in what you mean and say, you will live the blessed life."
"If a man were to conceive the existence of real goods, like wisdom, temperance, justice, fortitude, he could not with those in his mind still listen to the popular proverb about 'goods in every corner', for it will not fit."
"A virtue is none the less to be desired for its own sake, because it has some adventitious profit connected with it: indeed, in most cases the noblest virtues are accompanied by many extraneous advantages, but it is the virtues that lead the way, and these merely follow in their train."
"What a noble spirit it shows in a slave to have been willing to die for his master, at a time when few were faithful enough to wish their master to live! to be found kind when the state was cruel, faithful when it was treacherous! to be eager for the reward of fidelity, though it was death, at a time when such rich rewards were offered for treachery!"
"A man's joy is to do what is proper to man, and man's proper work is kindness to his fellow man, disdain of the movements of the senses, to discern plausible imaginations, to meditate on Universal Nature and the work of her hands."
"He who loves glory thinks the activity of another to be his own good; he who loves pleasure thinks his own feeling to be his good; he who has intelligence, thinks his own action to be his good."
"I speak of virtue, not of myself, and when I blame vices, I blame my own first of all: when I have the power, I shall live as I ought to do: spite, however deeply steeped in venom, shall not keep me back from what is best: that poison itself with which you bespatter others, with which you choke yourselves, shall not hinder me from continuing to praise that life which I do not, indeed, lead, but which I know I ought to lead, from loving virtue and from following after her, albeit a long way behind her and with halting gait."
"These considerations do not destroy the respect due to parents, or make their children behave worse to them, nay, better; for virtue is naturally ambitious, and wishes to outstrip those who are before it."
"Well, then, you must stand up in all this, kindly and not carrying your head proudly; yet understand that every man is worth just so much as the worth of what he has set his heart upon."
"For him whose sole good is what is in due season, who counts it all one to render according to right reason more acts or fewer, and to whom it is no matter whether he beholds the world a longer or a shorter time—for him even death has lost its terrors."
"I loudly and publicly proclaim that what I call a pleasant life cannot exist without the addition of virtue." Yet who does not know that the greatest fools drink the deepest of those pleasures of yours? or that vice is full of enjoyments, and that the mind itself suggests to itself many perverted, vicious forms of pleasure?—in the first place arrogance, excessive self-esteem, swaggering precedence over other men, a shortsighted, nay, a blind devotion to his own interests, dissolute luxury, excessive delight springing from the most trifling and childish causes, and also talkativeness, pride that takes a pleasure in insulting others, sloth, and the decay of a dull mind which goes to sleep over itself."
"Let virtue lead the way and bear the standard: we shall have pleasure for all that, but we shall be her masters and controllers; she may win some concessions from us, but will not force us to do anything."
"You Epicureans take pleasure in making a study of dull torpidity, in seeking for a repose which differs little from sound sleep, in lurking beneath the thickest shade, in amusing with the feeblest possible trains of thought that sluggish condition of your languid minds which you term tranquil contemplation, and in stuffing with food and drink, in the recesses of your gardens, your bodies which are pallid with want of exercise; we Stoics, on the other hand, take pleasure in bestowing benefits, even though they cost us labour, provided that they lighten the labours of others; though they lead us into danger, provided that they save others, though they straiten our means, if they alleviate the poverty and distresses of others."
"If a man should be able to assent to this doctrine as he ought, that we are all sprung from God 1 in an especial manner, and that God is the father both of men and of gods, I suppose that he would never have any ignoble or mean thoughts about himself."
"Even if what is nearest to it, your body, is cut, cauterized, suppurates, mortifies, still let the part which judges about these things be at rest; that is, let it decide that nothing is good or evil which can happen indifferently to the evil man and the good."
"Can what has befallen you prevent your being just, high-minded, temperate, prudent, free from rash judgements, trustful, self-reverent, free, and whatever else by its presence with him enables a man's nature to secure what is really his?"
"No one is moved by righteousness and goodness of heart to cultivate an estate, or to do any act in which the reward is something apart from the act itself; but he is moved to bestow benefits, not by low and grasping motives, but by a kind and generous mind, which even after it has given is willing to give again, to renew its former bounties by fresh ones, which thinks only of how much good it can do the man to whom it gives; whereas to do any one a service because it is our interest to do so is a mean action, which deserves no praise, no credit."
"Whatever any one may do or say, I am bound to be good; exactly as if gold or emerald or purple were continually to say this: 'whatever any one may do or say, I am bound to be an emerald and to keep the colour that is mine'."
"Make trial for yourself how the life of the good man, too, fares well, of the man pleased with what is assigned from Universal Nature and contented by his own just action and kind disposition."
"No, we have to consider this: what kind of soul Socrates had, whether he could be content with being just in his dealings with men and righteous in his dealing with the gods, whether he was neither hastily indignant with wickedness nor a servant to any man's ignorance, whether he neither accepted as unfamiliar anything assigned by Universal Nature or endured it as intolerable, nor submitted his mind to be affected by the affections of the flesh."
"It was necessary to insert this argument, my Liberalis, because it is the part of virtue to bestow those benefits which we are now discussing, and it is most disgraceful to bestow benefits for any other purpose than that they should be free gifts."
"Always bear this in mind, and further that to live the blessed life rests upon very few conditions; and do not, just because you have abandoned hope of being a thinker and a student of science, on this account despair of being free, modest, sociable, and obedient to God; for it is possible to become an entirely godlike man and yet not to be recognized by any one."
This was the most contested part of Stoicism in antiquity, and the Stoics knew it. Their own refinement was to rank the indifferents - health and money are 'preferred', worth pursuing, just not good in the way virtue is good. Critics then and now suspect the distinction is doing a lot of quiet work to keep an implausible doctrine liveable.
Read the passages with that in mind. Some hold the hard line without flinching; others, especially Seneca's, sound like a wealthy man explaining why his wealth does not count. Both are honestly part of the tradition.