The basic idea Seneca explains here is that a wise man is content with himself. And therefore needs no friends, or rather needs nothing except himself. Despite this, the wise man still desires things but does not “value” what can be taken away.
"apatheia... the man who refuses to allow anything that goes badly for him to affect him."
"Notice how self-contented he is: on occasion such a man is content with a mere partial self - if he loses a hand as result of war or disease, or has one of his eyes, or even both, put out in an accident, he will be satisfied with what remains of himself and be no less pleased with his body now that it is maimed and incomplete than whe was when it was whole. But while he does not hanker after what he has lost, he does prefer not to lose them."
"'I shall show you,' said Hecato, 'a love philtre compounded without drug or herb or witch's spell. It is this: if you wish to be loved, love.'"
"the wise man, self-sufficient as he is, still desires to have a friend if only for the purpose of practising friendship and ensuring that those talents are not idle. Not ... 'for the purpose of having someone to come and sit beside his bed when he is ill or come to his rescue when he is hard up or thrown into chains', but so that on the contrary he may have someone by whose sickbed he himself may sit or whom he may himself release when that person is held prisoner by hostile hands."
"These are what are commonly called fair-weather friendships. A person adopted as a friend for the sake of his usefulness will be cultivated only for so long as he is useful.
"What is my object in making a friend? To have someone to be able to die for, someone I may follow into exile, someone for whose life I may put myself up as security and pay the price as well."
"The wise man ... he lacks nothing, for lacking something implies that it is a necessity and nothing, to the wise man, is a necessity"
"We are impressed at the way some creatures pass through fire without physical harm: how much more impressive is the way this man came through the burning and the bloodshed and the ruins uninjured and unscathed."
"Not happy he who thinks himself not so"