There are a few good bits of advice and things to learn from this brief letter.
As mentioned in the previous letter about siren songs, Seneca reminds Lucilius to be mindful of those he chooses to associate with.
refrain from associating with men of different stamp and different aims. And I am indeed confident that you cannot be warped, that you will stick to your purpose, even though the crowd may surround and seek to distract you.
Focus is needed to make progress. As my current assignment at work deals with coaching our teams on agile, one of my favorite quotes, which we've turned into a sticker, is "start finishing and stop starting." We get so distracted by new things and ideas and initiatives. What we need more of is focus to finish what we've set our minds to.
And much harm is done even by one who holds you back, especially since life is so short; and we make it still shorter by our unsteadiness, by making ever fresh beginnings at life, now one and immediately another. We break up life into little bits, and fritter it away.
Start finishing your quest to philosophy and stop with new distractions. Life is short and when it comes to learning and applying your human craft, you have no time to lose. Death is on your heels; like an enemy chasing after you. The immediate goal is to "round out your life before death comes, and then await in peace the remaining portion of your time."
Learn to be content with little and give more to those in need - both materially and philosophically.
He makes an interesting comment about how Lucilius' parents prayed for many blessings on him. And in some warped paradigm, Seneca thinks that Lucilius' parents' prayers have "plundered" the blessings from others. "Whatever they make over to you must be removed from someone else."
I suppose if there were scarcity of some resource and if Lucilius' parents had such sway over the gods as to ask for said scarce resource that it be given to Lucilius and not another, then I guess the vice here is greed. But that only makes sense if the resource is scarce and his parents controlled the gods.
The more important lesson here, I think, is that his parents didn't know what good to pray for, for their son. Rather than praying for a scarce resource to be given to their son (and subsequently taken away from another), if they were to pray that their son be more just or have more courage or wisdom, I can't see how by granting their son with more virtue, the act takes away from others! In sum, if you are going to pray, don't make it a Santa Clause wish-list of indifferents. Pray for something the gods give (and have already given) in abundance: virtue.
The amazing things about the good is that once you learn it and truly grasp it (think of a fist tightly grasping something), you have it immediately. The work is in the learning and being truly convinced.
I pray that you may get such control over yourself that your mind, now shaken by wandering thoughts, may at last come to rest and be steadfast, that it may be content with itself and, having attained an understanding of what things are truly good, – and they are in our possession as soon as we have this knowledge, – that it may have no need of added years.